I don't appreciate when more than 1 members keeps saying that my price is too high repeatedly on the same post but some members too seem interested in buying the product/account. Quickseller's post dint seem off topic as he showed interest in buying the account but if he keeps saying the same thing on other threads, it would be considered only spam.
He might be looking for better buying options, and so what's the harm in saying the same thing on different threads? After all I don't think his signature pays for them.
A normal person wouldn't repeat the same post on all threads (and not all selling threads quote high prices). If one does it they are either getting benefitted from their post or are just trolling. There is a PM option too and if one is interested in buying, they can bargain with the user via PM.