What is the best way to warn others about this situation?

You should contribution for moderator attention by using a custom flag. If you believe the contribution to be spam, you should flag it as spam, if a moderator does not agree they will simply decline the flag.

The typical user coming to help from this site could easily fall victim to the scheme, and my question, therefore, provides an effective advertising platform for their product.

Leaving a single comment saying the answer was unhelpful. You should avoid having a discussion if the other person believes your comment isn't helpful. If they leave a comment you believe to be rude, you should flag the comment, so a moderator can deal with that behavior.

Because I could not find how to complain or warn others, I responded as you can see here. But I would appreciate someone in authority at the site to provide me with a proper way to complain about this situation and warn others.

Creating a meta question will also bring the unhelpful contribution to the attention of others. There is nothing else that needs to be done.

I do not see how to use "a custom flag" on an answer.

You should be able to select that option.

What is the best way to warn others about this situation?

You should flag the contribution for moderator attention by using a custom flag. If you believe the contribution to be spam, you should flag it as spam, if a moderator does not agree they will simply decline the flag.

The typical user coming to help from this site could easily fall victim to the scheme, and my question, therefore, provides an effective advertising platform for their product.

Leaving a single comment saying the answer was unhelpful. You should avoid having a discussion if the other person believes your comment isn't helpful. If they leave a comment you believe to be rude, you should flag the comment, so a moderator can deal with that behavior.

Because I could not find how to complain or warn others, I responded as you can see here. But I would appreciate someone in authority at the site to provide me with a proper way to complain about this situation and warn others.

Creating a meta question will also bring the unhelpful contribution to the attention of others. There is nothing else that needs to be done.

I do not see how to use "a custom flag" on an answer.

You should be able to select that option.

What is the best way to warn others about this situation?

You should contribution for moderator attention by using a custom flag. If you believe the contribution to be spam, you should flag it as spam, if a moderator does not agree they will simply decline the flag.

The typical user coming to help from this site could easily fall victim to the scheme, and my question, therefore, provides an effective advertising platform for their product.

Leaving a single comment saying the answer was unhelpful. You should avoid having a discussion if the other person believes your comment isn't helpful. If they leave a comment you believe to be rude, you should flag the comment, so a moderator can deal with that behavior.

Because I could not find how to complain or warn others, I responded as you can see here. But I would appreciate someone in authority at the site to provide me with a proper way to complain about this situation and warn others.

Creating a meta question will also bring the unhelpful contribution to the attention of others. There is nothing else that needs to be done.

What is the best way to warn others about this situation?

You should contribution for moderator attention by using a custom flag. If you believe the contribution to be spam, you should flag it as spam, if a moderator does not agree they will simply decline the flag.

The typical user coming to help from this site could easily fall victim to the scheme, and my question, therefore, provides an effective advertising platform for their product.

Leaving a single comment saying the answer was unhelpful. You should avoid having a discussion if the other person believes your comment isn't helpful. If they leave a comment you believe to be rude, you should flag the comment, so a moderator can deal with that behavior.

Because I could not find how to complain or warn others, I responded as you can see here. But I would appreciate someone in authority at the site to provide me with a proper way to complain about this situation and warn others.

Creating a meta question will also bring the unhelpful contribution to the attention of others. There is nothing else that needs to be done.

I do not see how to use "a custom flag" on an answer.

You should be able to select that option.