I'm only speaking for myself here, although there are probably others who have been in the same situation as me...
When I sell a knife these days it's because I need the money. Often I need it in short time, because I'm not the most fiscally responsible or I cut things way too close (ie: rent to pay).
If I'm selling a knife and initially ask $325, and I get 2 offers: Person A for $325 and Person B for $300. Both say "I'll take it", Person A for $325 is first, but the one for $300 says he can pay immediately. Naturally, I'd go with the Person A, tell him where to send the PP, etc.
But then Person A flakes out in some way. It'll be a couple days before he has the money. Or he changes his mind. Or worse, there's no further communication, at least for a couple days.
Shoulda just sold to Person B, right? I would be sorely tempted to give Person A negative feedback.