After dealing with both types of offers this year 
for the first time, both for very high wishlist 
cels, I found the one-time offer deal to be much, 
much less stressfull. You make your offer, and 
you either get it or you don't. I just made the 
offer that I felt the cel was worth, and I 
figured if I lost then at least I tried my best, 
and I wasn't pressured to pay more than I wanted 
to, causing me to regret the cel later. In both 
cases I got the cel I wanted, but the one-time 
offer one cost me much less, and was a far better 
experience buying wise. Even the seller told me 
that they went with the one-time offer deal 
because it was a much easier approach to selling, 
and less time consuming.