Depends on your threat model. If you're concerned about the inherent well-known conflict of interest in the industry, it's probably sufficient to ask (a key word is fiduciary - are they a fiduciary or not?). The general pattern for commissioned financial advisors isn't optimal for you as a client, but it isn't fraudulent. There's also an organization called NAPFA [0] that registers fee-only advisors.

If you're worried about a malevolent actor who's willing to commit fraud and openly lie, well, how do you deal with trust for any other kind of professional? Reputation, credentials, reviews, referrals, word-of-mouth, etc.

You can also seek advice from someone independent of handing them your money to invest. You can ask an advisor to tell you what you ought to be doing with a self-directed brokerage account at another firm. I guess it's not impossible that there could be an elaborate scheme to collect commissions even across institutions, but again, you need some sort of trust for the whole project to make any sense.

[0] https://www.napfa.org