This is indeed a tricky situation.
I have a webmaster site with the appropriate community :lol: I allow my members to link to their webmaster site/forum in their signatures (I mean something discreet and of common sense, not "Join now", "visit now" ...
I allow web site reviews. In the end I have started the entire project after getting involved in other huge forums and reviewing sites. After a while I thought I should have a site of my own where i can express MY own views on design, layouts, promotion and so on. After putting down some very "opinated" articles I have thought about starting a forum too.
I allow reviews there too (well, it's my "job"

). BUT .. I don't allow forum reviews. Why? because most of the time people post there just to promote. Unless I see some serious theme modding and efforts to make me have what to review, I just consider it a sneaky way to get visits and members. When someone installs a script and uses a stock template, then he should be prepared for some "nasty" remarks.
I do allow forum reviews in my "group" called Forums development team". Usually people who want to get more members and posts join, make 20 posts and ask for inclusion in the team. The team is hidden and so is the corresponding forum. That's the only way I am willing to give tips for improvement and reviews.
As for the other sites, they are reviewed in the "normal" reviews forum. If I am not mistaken I have made it so only people with more than 20 posts can post there and open topics. Same for the "market" place. I don't want my place to become a spammer's heaven, nor turn it to a "shopping place". The members who are "serious" enough as to post 20 messages (takes me 30 minutes to do so

) are allowed for more "goodies".
Not a good idea if you want to fast expand, but in the end I don't rush anywhere. I want more posts and quality then just people to waste my space and bandwidth ...