I came across few situations in recent days some module developers digging in old questions or the questions which are related to their developed module and using comments and answers to advertise their modules I flagged some of them which were done on the answers of mine but how to stop them doing this?How to keep MSE away from this kind of things?
First take a look at the user profile. If you see that all of the answers (or almost all of them) are self promoting, flag one of their answers for moderator's attention and fill in a message saying "This user only self promotes". You can even put the link to the user profile.
Most probably their accounts will be suspended temporarily or deleted.