I was not aware that Amex would tell you their internal limit. They'll run a test charge for you and let you know if that charge will go through, but I don't think they'll tell you the exact amount that you can spend up to.
I don't think you need to worry about it. It's always wise to have an alternate form of payment for any credit card. If you don't have an alternate form of payment, I'd be a little more careful about how much I was spending on the card, but I really don't think it is a big deal. You can authorize a payment over the phone if you do run up against your limit and they will release the funds.
Starting Score: ~500 (12/01/2008)
Okay, so here's MY PERSONAL EXPERIENCE as an AU on my partner's AMEX. About two weeks after he received the card, he added me as an AU. Since I shop more than he does, I used the card more (I think he had only charged about $800 immediately after he received it). Well, I used it for everyday use on almost everything including small purchases like coffee, McDonald's, etc. (rewards hungry) and spent about $2700 about three weeks after I received mine and PIF about two weeks after using it. The following month, I charged $1,400 and he didn't use his at all. About two weeks later, I went online to pay the bill in full and received a "Charging Suspended. Please call....." I immediately called him and told him what happened and they threw him under Financial Review. It was a pain in the ARSE for him AND for me because although I could still pay the bill, we couldn't use the card (lesson learned in realizing the power that these companies have over you in a HEARTBEAT). I went ahead and paid the bill in full (I certainly wasn't going to leave him hanging because we couldn't use the card) and let him handle AMEX. Their reasons for FR: 1) The AU was using and paying the card more than the primary user; and 2) the AU was using the card like a debit card to make small purchases (i.e., Starbuck's McDonald's, etc.)! I didn't think it should matter because if the primary user has provided the AU to use the card and the bill was paid (WELL in advance of the due dates) BY THE AU, everything was cool...NOT! We couldn't use the card for three weeks while he was under. Fortunately, we both have back-up cards and cash and we were STILL AT HOME when all of this happened (I've heard some SERIOUS horror stories about people being miles away from home and out of the country when this has happened to them). Handle your card however you want...just know that someone shared their AU story with you.
@sybo40 wrote:Okay, so here's MY PERSONAL EXPERIENCE as an AU on my partner's AMEX. About two weeks after he received the card, he added me as an AU. Since I shop more than he does, I used the card more (I think he had only charged about $800 immediately after he received it). Well, I used it for everyday use on almost everything including small purchases like coffee, McDonald's, etc. (rewards hungry) and spent about $2700 about three weeks after I received mine and PIF about two weeks after using it. The following month, I charged $1,400 and he didn't use his at all. About two weeks later, I went online to pay the bill in full and received a "Charging Suspended. Please call....." I immediately called him and told him what happened and they threw him under Financial Review. It was a pain in the ARSE for him AND for me because although I could still pay the bill, we couldn't use the card (lesson learned in realizing the power that these companies have over you in a HEARTBEAT). I went ahead and paid the bill in full (I certainly wasn't going to leave him hanging because we couldn't use the card) and let him handle AMEX. Their reasons for FR: 1) The AU was using and paying the card more than the primary user; and 2) the AU was using the card like a debit card to make small purchases (i.e., Starbuck's McDonald's, etc.)! I didn't think it should matter because if the primary user has provided the AU to use the card and the bill was paid (WELL in advance of the due dates) BY THE AU, everything was cool...NOT! We couldn't use the card for three weeks while he was under. Fortunately, we both have back-up cards and cash and we were STILL AT HOME when all of this happened (I've heard some SERIOUS horror stories about people being miles away from home and out of the country when this has happened to them). Handle your card however you want...just know that someone shared their AU story with you.
That's a scary story. To your point, why should they care if the AU spends more than the primary? As long as its paid it shouldnt matter. AMEX saw big spending so for them that was a red alert but again as long as its paid who cares?
What card are you an AU on if i may ask?
@sybo40 wrote:Okay, so here's MY PERSONAL EXPERIENCE as an AU on my partner's AMEX. About two weeks after he received the card, he added me as an AU. Since I shop more than he does, I used the card more (I think he had only charged about $800 immediately after he received it). Well, I used it for everyday use on almost everything including small purchases like coffee, McDonald's, etc. (rewards hungry) and spent about $2700 about three weeks after I received mine and PIF about two weeks after using it. The following month, I charged $1,400 and he didn't use his at all. About two weeks later, I went online to pay the bill in full and received a "Charging Suspended. Please call....." I immediately called him and told him what happened and they threw him under Financial Review. It was a pain in the ARSE for him AND for me because although I could still pay the bill, we couldn't use the card (lesson learned in realizing the power that these companies have over you in a HEARTBEAT). I went ahead and paid the bill in full (I certainly wasn't going to leave him hanging because we couldn't use the card) and let him handle AMEX. Their reasons for FR: 1) The AU was using and paying the card more than the primary user; and 2) the AU was using the card like a debit card to make small purchases (i.e., Starbuck's McDonald's, etc.)! I didn't think it should matter because if the primary user has provided the AU to use the card and the bill was paid (WELL in advance of the due dates) BY THE AU, everything was cool...NOT! We couldn't use the card for three weeks while he was under. Fortunately, we both have back-up cards and cash and we were STILL AT HOME when all of this happened (I've heard some SERIOUS horror stories about people being miles away from home and out of the country when this has happened to them). Handle your card however you want...just know that someone shared their AU story with you.
Wow. That's exactly how I use my cards - I put everything on them including small stuff and I PIF. No AA from my cards and, in fact, I'm receiving CLI's and APR reductions.
I don't have an AmEx, but it's on my list for next year. Who knew this type of behavior was a red flag for them? 
Golly.