I've been helping with the following question:
But another user has answered offering professional services. What is the feeling about this, is it allowed? Encouraged? Or should it be flagged?
Do you feel greasier having read their post about offering services and asking you to contact them offsite instead of just giving an answer?
If so, that's most likely spam. You can flag it as spam if you feel a solicitation is happening here. That's not allowed and explicitly discouraged.
If they work on or with the product and mention their affiliation, then that's usually case-by-case depending on how they push their product in relation to answering the question. Most of the times these are allowed given the note.
For others, if they want to advertise they can either: