A quick test is to see if it's a first post from a new member. Any such post which contains a link, or clearly invites one from another new member, is suspect.
The use of Asian English (e.g. 'Please suggest me . . .') is also a tell-tale sign, as are certain patterns of usernames. (We seem to have several spammers who think that a 'forename + surname' username, possibly with a number on the end, looks genuine. So we get spam from 'ArthurHendricks, 'MoiraTwigg001', etc. The reality, of course, is that very few 'genuine' members use their real names).
When I suspect possible '2-part' spam is on its way, I post a 'moderator's note', as here:
http://www.theanswerbank.co.uk/Travel/Question1441082.html
However sometimes spam is so blindingly obvious that I'll simply ban the poster directly.
Moderator's aren't perfect though. (I'm certainly not!). Another mod does seem to have banned a regular contributor (XingWang) this morning, purely because his post looked a bit like spam. (Oops!)