I have answered a question recommending a product I'm developing.
I have looked around here, and in the FAQ, and the only thing mentioned is to clearly state your affiliation in the post. I have done that, however, I'm still a bit uncertain about the part where I mention the rates (prices).
Personally, when reading SO answers mentioning software I divide them by the following criteria: opensource or not. Following that line of reasoning, I find it dishonest to recommend an API (be it mine or not) and not to mention that, it is free-of-charge during the beta testing only.
I might be overreacting, but I'd really appreciate your thoughts on the matter.
About "mentioning the prices" - this is the only sentence in the answer reffering to that:
"The API usage is free during the beta testing phase"
After the OP gave feedback, it became clear that it was a matter of wrong judgement, so I updated&reformatted the answer, removing the references to commercial product completley.
As for the my original question, I think it was wrong judgment in the first place. If the OP asks specifically for commercial service/product, or it is clear that he needs one (which was absolutley not the case here) then I think it is acceptable to acquaint him with a commercial product. The only situation I have seen in practice on SO like this is the telephony and SMS API's, so I believe these are rare situations here.
Thanks for your answers.