Weight is not important to me because I can easily deal with the weight of any common bass I have ever owned or played in a store. If I offer a bass for sale on TB I will post the accurate weight, usually on my own, certainly if asked for it because I know a lot of TB members are as concerned about weight as a bicyclist and many of the rest have caught the weight weenie disease from them. People who are selling a bass do not appreciate it when someone does something to poison their sales effort. Asking for the weight and then saying no thanks, that's too heavy, as many potential buyers will because it seems polite will be viewed by some sellers as a criticism of the bass that they are selling. That is probably why they mock you for asking. To them it puts a better spin on the situation than having someone say there is something wrong with their bass. The thing is that people will be influenced by your comments even though they may have no reason to reject a bass that weighs 9.6 pounds, or even 12. But if someone else says 9.6 is too heavy and they have never given much thought to weight they will have second thoughts.
To sellers I would say post the weight up front because that gives potential buyers the information they need and lets them quietly move on without offering any comment on your bass. If you forget and someone asks then just answer their question without comment.
To buyers I would say do not EVER comment on your personal weight limit in a for sale listing. It is fine to ask for the weight if it is not given but do not react to the weight when the seller responds. A lot of buyers ask questions and then don't buy the bass. As long as you don't comment about the answer to any question that you ask your questions are neutral. Buyers have many, many reasons for deciding they aren't really interested and their disinterest does not affect the next buyer's decision. Buyers who openly comment in a negative way on a bass for sale do potentially affect the decisions of the next potential buyers however and so you can expect sellers to react poorly to this kind of "help".