seems to me there are two distinct kind of posts:
1. A response to a specific query, e.g. somebody asks for a deal on a specific ticket and "you" answer "I can get it for you for $x", which seems to me (not that my opinion is what counts) would be ok.
2. Randomly offering your services e.g. "PM me for the best prices on flights to Israel for Pesach" which I imagine is the same as any other advertising which is not allowed.