[quote name='SevereTireDamage']If you're a good seller, you should definitely send positive feedback as soon as you get payment, immediately if you're getting it through Paypal.
If you're a buyer, you leave feedback as soon as you get the stuff and checked it out so it's all good.
What's so hard about this? I don't know.[/quote]
Here's a good reason. Let's say someone pays, you send the item, then they claim they never received it and you have already left positive feedback. Or they claim it wasn't in the advertised condition. Or better yet, they claim it doesn't work when really it does. Or there are the wonderful bidders who win a game that is pictured AND described as "with video stickers" or "with writing on it", etc. but when they receive the item demand a partial refund because it's not as nice as they had hoped.
Sellers have to protect themselves from underhanded bidders just as much (if not moreso) as vice-versa. I have had some bidders completely flip out for no reason and been very glad that my feedback was holding them back from just negging me and going about their business. It's nice to be able to email someone back and say "If you're not going to act respectfully I don't have to deal with you." When you've already left feedback you are completely at their mercy.
The deal is only 1/2 over when the bidder pays. There is still a LOT the bidder can do to make it a negative experience after they have paid a seller. If you sell something and you leave positive feedback as soon as they pay, you're begging for someone to take advantage of you. Yeah, yeah, boo hoo - a seller can use the feedback to force a less-than-happy bidder to leave better feedback than what is deserved. Be a man (or woman) and leave whatever feedback is deserved. If someone tries to blackmail you and you fall for it, it's your dumb fault.