I have a lot of bidding experience, but not a lot of
winning experience

Clearly if c***3 bid even once cent more, you would have lost to him. I don't blame you for feeling paranoid, but there are a number of factors that explain what happened, not the least of which is that $500 is indisputably a round number.
Having won very few auctions I sympathize with anyone who perceives someone came along and did nothing more than drive up the price you had to pay

but that's the way it goes. My advice is always to simply
bid the highest amount you are willing to pay, not one cent less, knowing that you might actually have to pay it.
Then, be happy you won. That's what happened, so be happy!