I've had 100% feedback since 2002 and do anything within reason to keep it. I have followed through on purchases that I wished on second thought I hadn't made. I have asked to back out of a few but will buy if the seller insists. When I like an item I leave positive feedback. If I'm disappointed I leave no feedback rather than negative feedback. Maybe a private message but no public criticism.
What I have learned about ebay is that many sellers know nothing about what they're selling. They have no use for it and they just want to move it. There are some rip-offs, but I believe most of them are unintentional. Perhaps a high price is based on what he paid for it.
A guess of what I think happened to you is that he put an item up for sale and a spouse or friend have given him a lot of grief over it and he relented to shut them up. You're within your rights to report it to ebay and try to hold him to the bargain but I'm not sure I'd want something grudgingly surrendered. He might give you a damaged item as a form of revenge. And his life may not be peaceful for a while because of the grief his family or friend will give him.
Some sellers are embittered and feel worn down. One was selling a nice razor for $35 or Make Offer. I asked him how low he'd go and he said $30. He added that he paid $40 for it, and was incurring fees to keep it listed. I gave him $35. We each lost $5 on the deal but $35 for a nice vintage shaver is a great deal as far as I'm concerned.
I give and take to get along and hope the other party does the same.
Ask him how much he wants for the razor and decide if it is worth a modest increase. There have been a couple of occasions I have made a counter offer or offered to pick up his PayPal fees which in this case might be a dollar or less.
The machinery works better at ebay when parties reach out to one another.