Let me to give you a non-financial example. Authors often send free copies of their latest work to book critics. Under US Federal Trade Commission (FTC) rules, the critic may discus the book and be positive or negative about it. If the critic fails to disclose that a free copy was provided, this is not only unethical, but also illegal under FTC rules. Many other countries have similar rules.
If you offer compensation, even without restrictions on the content, that increases the chances of a more positive post. Would you think it fair if one of your competitors offered a no deposit bonus and required the people to leave reviews at the FPA in exchange for having those accounts activated? It's happened, and I've taken action when it did. In this case, you've narrowed the field down to those who not only got a no deposit bonus, but also profited from trading it. Are those representative of all of your clients?
Offer all the bonuses you like. Just be aware that if I ever see any future compensation for any type of post or review, this will result in an immediate warning on the FBS review page.