If you're dealing with a scammer who's not afraid to blow $40k a pop on chartered jets, there's nothing stopping them from creating a pretty website that shows fake portfolios composed of real prices of real assets they haven't actually bought.
(And yes, a few tiny PWM firms do use their own Web sites, and you should be much more skeptical of the data you're getting from a 6-employee firm's site). Get access to your custodial account at a name-brand firm's site, or change asset managers.)
Also, they'll appreciate that you're doing this due diligence. If you get any pushback, move on.
Also worth noting that this problem is mostly moot for a typical retail investor who has assets at a name-brand brokerage like ETrade, Schwab, or TD Ameritrade, and already has self-service access to the bank/brokerage's site. At that point, an individual advisor might be able to make unilateral allocation changes, but the money's there and the bank will have a trading history. This problem in this article basically starts with trusting a lot of money to an individual or tiny firm, and that basically only comes up in PWM and non-traditional asset classes.