This does come up from time to time, in fact there's a bit of a sagaa bit of a saga related to self-promotion on Meta Stack Overflow.
If your company has products that are directly related to the topic of the site, it's generally okay to recommend them if:
- You answer the question directly. E.g. "This is my product, this is how you use it, and this is why it might be a good choice."
- You clearly indicate that you are the author or beneficiary of the product or site
- The vast majority of your answers do not mention your product or services
- You refrain from promoting your product where it's at best tangentially related to the question
Those rules provide a rather narrow window where this sort of thing might be acceptable. But they apply mostly to established products, something that someone could go download and conceivably start using right away. This was established for libraries, game controller modifications, and other things.
When your product is yourself, this gets a little tricky. This is what I'd recommend:
- Don't ever outright say "contact me off site so we can arrange something"
- Don't answer the question unless you can tell them (roughly) what they need to build, and perhaps where they could get started - you need to answer the question
- Do make certain that you let people know you do custom work, in your user profile and have some means of contacting you there
- Do Take advantage of the fly-out user card summary line to alert folks that you are for hire if they need help
This lets users know that you can help them out, and how to get in touch with you without being shady or spammy. Users put everything from PayPal donate links as a 'tip jar' in their profiles to Amazon wishlists - that's nothing new. If you write awesome answers and know your stuff, people will see your details and availability.
You can promote yourself or your products, you just have to be very careful when doing so, and make sure it's your awesomeness that draws people to them, not just links ;)