Of course every big sale required a lot of turned down offers to get to the final sale price, so those are too many to even count or think about.
A better clarification would be, what was the biggest offer you turned down that didn't end up in a sale, and, did you regret it? I'll have to put some thought into that one.
I had an 8500 CAD offer a couple weeks ago that I kinda regret. The buyer was so pissed off he changed his mind, called me a few choice words and something about karma. I wasn't going to entertain that kind of behavior any further. But I could have just accepted the 8500 and been OK with the sale. But I still have a great domain, he still has his $8500.