Whether the OP has interesting information or experiences, regardless of your personal opinion of that person or their experiences. The Westboro Baptist Church is a good example; even if you vehemently disagree with their viewpoint, they still have a very uncommon perspective to share. Downvoting the OP because you disagree with them will only result in an undesirable atmosphere and will likely end up with OP ending the AMA early, or not put effort into answering questions. Rather than downvoting, which just hides the comment from being seen by anyone, offer a reply with your reasoned thoughts. This way, you can open a dialogue with OP and potentially debate the differing points of view.
Upvote for providing proof in the post. If there is no proof, ask for it! If the OP ignores requests for proof, or just dismisses it, then report it to the mods.
Once it has started, how they are responding to questions overall. If you feel that they are only here to plug a product and didn’t take the time to interact with the community, then feel free to downvote it.