It is not generally appropriate. In this case, imho, it is borderline acceptable.

I've got a 6 point test to determine if the account is a dirty spammer who needs bannination:

1. Is the user posting from an unregistered account?
2. Does the user have a fully-fleshed profile with full disclosure in the "About Me"?
3. Is the user a hit-and-run answerer?
4. Has the user added new answers to old questions in order to pimp their product?
5. Has the user added answers to questions with an accepted answer in order to pimp?
6. Do the answers contain no information except a link to the product or blog?

As for Mark:

1. No, he is registered and has been a member over a year
2. His profile is fully fleshed, with full disclosure
3. Slightly. No questions, averages one answer per month, and has only cast two votes.
4. Only once.
5. Possibly 1-3 times, but they are close
6. No, in fact his answers are particularly detailed and long

While it would be nice if he were more active in other respects, his answers are on topic, are detailed and not rubber stamped across all possible matching questions. He is very clear about disclosing his relationship with the product, both in his answers and in his profile. So, I would not consider him a dirty spammer worthy of the ban. Not the best member of the community, no. But nowhere near the bottom of the heap.

It is not generally appropriate. In this case, imho, it is borderline acceptable.

I've got a 6 point test to determine if the account is a dirty spammer who needs bannination:

1. Is the user posting from an unregistered account?
2. Does the user have a fully-fleshed profile with full disclosure in the "About Me"?
3. Is the user a hit-and-run answerer?
4. Has the user added new answers to old questions in order to pimp their product?
5. Has the user added answers to questions with an accepted answer in order to pimp?
6. Do the answers contain no information except a link to the product or blog?

As for Mark:

1. No, he is registered and has been a member over a year
2. His profile is fully fleshed, with full disclosure
3. Slightly. No questions, averages one answer per month, and has only cast two votes.
4. Only once.
5. Possibly 1-3 times, but they are close
6. No, in fact his answers are particularly detailed and long

While it would be nice if he were more active in other respects, his answers are on topic, are detailed and not rubber stamped across all possible matching questions. He is very clear about disclosing his relationship with the product, both in his answers and in his profile. So, I would not consider him a dirty spammer worthy of the ban. Not the best member of the community, no. But nowhere near the bottom of the heap.