There are so many things people get up set about after the fact that could (should) have been settled before the transaction took place. You know the list: "I assumed it would be sent insured;" "I thought you would use Priority Mail;" "I didn't know it did not have the factory box and paperwork;" etc.
This is another.
If you are a buyer, and you want your identity and the selling price or even offering price kept private/removed, you should negotiate that with the seller BEFOREHAND as part of your offer. Real easy. "Joe, will you take $200, and I 'd like my identity and all price information removed and kept confidential. Do we have a deal?"
I don't think there is much cause to be unhappy about something that you didn't work out beforehand.