I've never been turned down for CLI on my WFB Visa (I've asked for one at least 1x per year), but they always reject my APR adjustment requests. My credit situation is slightly different and I have no derogs in my credit or in my pay history with them, so YMMV.
Right now my credit line with them is $9000, it used to be $6750, before that, it was $3750. I usually only request CLI bumps of 25-45% of the current credit limit, and the time I ask is when I have no more than 25% utilization. They have always auto approved after asking a couple simple questions like current yearly salary. I could probably be approved for a much higher credit limit, but I never bothered trying to push the limits of what I can have available to me.
Additionally, I have used the card extensively, which may or may not come into play with their approval. For each tier of credit limit, I have at one time used 75% of it (High Balance), and then paid it down. I'm unsure if someone has a low High Balance on a card with a high credit limit will get approved (ie: $1000 High Bal on a CC with a $10,000 limit)
