If i leave him a negative feedback on his ebay account, would that have any interference with the paypal investigation?
I've always looked at the initial downpayment on the eBay Motors part of eBay as something nonrefundable, but that's just my view. This other guys view from what I've seen of his business via his eBay auction is strictly via the internet, he has no showroom, only a storage warehouse. Anyone should agree that he's bound to feel that when someone like you comes along and bids, then sends in a downpayment, that they've honestly decided they're serious about purchasing his item.
I also do know that when you confirm your bid on eBay that eBay considers that confirmation as a contract for you to fulfill your commitment to purchase. I think right now it's all balancing on whether or not this guy is generous enough to work with you or not. I'm not trying to be rude here, only honest, because you've come here asking for our opinions. As I see it from my side you've tipped the scales all the way over to the wrong side for yourself in this situation by bidding, sending in your downpayment, and then wanting to backout!
As someone else also said, at the very least you are most definitely owing him all of his eBay listing fee expenses, as well as any Paypal deductions for monies sent to him, which may include "make ready" fees also since he was expecting you to honor your bid, as anyone would, because you showed sincere interest by getting your deposit to him up front!
This isn't his fault and personally I think for you to post negative feedback against him would be 100% wrong. I can't see where the seller has done anything to deserve that from you because you decided to change your mind! All he did was provide an auction, which you bid on it and sent in a deposit for! I mean how can you blame him in any form or fashion? All he was doing was carrying on his business and certainly not expecting after you bid and paid the downpayment that you'd back out. In my view that's not enough reason for you to mess up his spotless record with negative feedback because you changed your mind.
The one thing I've learned in my nearly 56 years on this planet is that when you're wrong the only right thing to do is just man up to it and accept the fact, that if you cost someone else money and time from your mistake, or in this case your changing your mind, no matter the reason, then you make it right. I don't know your age but the one thing in this world I've learned over my years is that integrity and honor are two of the main things that makes you a real man in this world, and to strike back and someone else for something you caused damages you, not them. Truth, integrity, and honor make me feel cleaner than any soap ever has in this world, and that if you live by those standards instead of corrupting your ownself just over money, then you'll live a better life with more people looking up to you!
Everyone in life has had something come up unexpectedly forcing them to change their plans. Whatever happened that caused you to change your mind on this purchase isn't the sellers fault, so why should he suffer with negative feedback because of what's happened in your personal life? The ball is in your court, for your own sake I hope you make the right choice, in the long run you'll be much more proud of yourself for doing the right thing and people will look up to you for having done so!
That's just my 2 cents JB, I'm not an attorney but I've been around enough years to know the difference between right and wrong.
Good luck and take care,
SnowCajun