There is definitely a risk. As we have just recently seen, clients were arrested when an agency (which, IIRC, advertised on terb) was busted.
Now, there may very well have been reasons to bust that particular agency, and there may very well have been red flags for hobbyists to stay away (don't know, that place was never on my radar).
Now, we may like to think that everything is on the up and up at <insert favourite MP here>, but the fact is, we really don't know everything that goes on "behind the scenes". This business can, at times, be ruthless, and if you've been around long enough, you've probably heard some stories (always take with a grain of salt.. consider the source and their motivations!) and maybe have a few of your own to tell.
I think we can probably make some reasonable assumptions about which places may be safer (not necessarily safe), as police seem to be picking off what might be considered the "low hanging fruit".
But the fact is, a lot of what happens in a MP is arguably verboten under C-36 (or, at least, LE may interpret the law in that way), and so there is risk. The question you need to ask yourself is.. is the risk worth the reward? Personally, I've decided it's not (along with other factors) and I've been sitting on the sidelines. But obviously others have made a different choice.. and so far it's worked out just fine for them.