IMO, offer 100%. Here's why: DW had a JDB (Wolpoff & Abramson) purchase a legit debt owed to Cross Country Bank (who later became Applied). The debt was for about $750 or so. We negotiated (years ago) 20% or 25% off in return of it being deleted and settled as if the debt was paid in full.
W&A accepted the offer and all seemed well. To cover out butts we sent a certified check and sent everything CMRRR. Over a year later we get a new CA notice for the settlement difference from a new CA. We wrote back and stated we settled and included copies. They responded that they don't acknowledge other CA agreements but they did go away.
Then that CA sold it to another. Then another and then another until it found its way back to Applied, where it still sits today 7 yrs and 4 months after DOFD. One CRA will remove hopefully this week (5/08 removal) and the other (EQ) should be the same.
Point is, I do not trust CAs. Yes, we could have taken more steps to prevent this (ie.e threaten lawsuite, report to BBB, FTC or others). But I still don't trust them. Unless your debt is so large, in the thousands where 20% could make a significant impact budget-wise, then I would offer 100%.