@whooami: Thanks for your input (as well!) :)
I would definitely agree that something like this shouldn't have to be enforced and become a burden to the moderators. Hopefully it can be encouraged as good practice, even though it may only work some of the time.
Maybe a disclaimer that is as simple as 'I am the developer of the plugin' or 'this is a commercial plugin'.
p/s: To elaborate, the main reason I started this thread is after seeing a few people posting commercial plugin recommendations (I'm sure one or two had really good alternative 'free' plugins) that were disguised self-advertisements (that sounded dodgy) once one looked a little bit deeper, even though it probably wasn't obvious to new users.
Commercial plugins do have a place in the WP community, but as a strong believer of open source/creative commons plugins (and inevitably, free! :p) I think dubious advertising of commercial plugins should really be discouraged on the Forums, to minimise the chance of someone being inadvertently duped into a dodgy purchase.
p/s2: Any suggestions for an alternative to 'Should'? :D