It's a personal choice:
If you don't have a FT set, ignore the post and report it as spam if you want
If you don't want to PM them FT, you don't have to
If you'd rather post the FT in the topic, sure, do that
I think what you're asking is to remove the negotiative element to trading and make it binding and fixed... which I think makes things boring and uninteresting. I actually find the ability to haggle fun, and allows me to gain more profit from trades and such. It also seems like you're pressuring people to make FTs, which is unfair because some people don't know prices or it might be some insane rare that they want to see offers on first