It is a leap of faith when you rent direct. The good news, we very rarely have any reports of people getting ripped off on the direct rentals. Usually it's more so missing amenities, or not quite up to par we hear about. Even then, that is rare.
You can check w/ the BBB. Also, you can check w/ the homeowners management company. If the housing development has a mang. office, you can check w/ them too. You could check past references from "past guests". However, lets be somewhat honest here. Those people you are checking w/ can claim to be anyone anywhere in the world who had a great exp in the rental unit. When in reality they could be the owners spouse w/ a cell, or their brother who lives 1/2 way across the country. So, I've never checked these references, because there's just no way to know for sure. Also, check the county tax rolls to be sure the property exists and is owned by the person you're dealing with.