I had a similar experience a couple of months ago. When the receptionist at my eye doctor ran my DL Amex, she told me it had been denied. I asked her to try again and it went through the second time. The next day I noticed two identical charges in my pending section, so the first must have gone through despite the denial. I decided to wait and see what happened, and only one of the charges ever posted. IME, Amex handles these better than some other companies. I've heard people saying that with some cards they were denied because they visited the same store twice in the same day. Much easier on me if they let things that aren't outright red flags go through and then sort them out while they're still pending.