I've been searching - with OCD fervor - for Rome rentals and know for a fact that some of Italy Perfect's Rome properties are represented by more than one agency or are actually serviced-apartments-hotels bookable in several ways. However, it's my understanding that these agencies sometimes are the exclusive company listing a particular rental (I've found this in instances with Sleep in Italy and Rome Accommodation, where it's their agent that's onsite when you check in versus the apartment's owner) but would be surprised to learn that they actually also owned the properties.

I agree with you about the hit and miss of VRBO, Homeaway, Homelidays, etc since they're all independent and can disallow bad reviews from showing on those sites.

Working with a trusted rental agency is very advantageous, for all the obvious reasons, and therefore well worth the additional cost - I agree.

Unless you found a listing represented on a reputable agency site with many positive reviews and with many positive mentions that the owner was great/helpful/responsive to issues that arose - and then you found that same rental listed by the owner himself on VRBO and for far less cost - then that's a great find and a fairly safe bet to proceed. IMO.

But re VRBO, etc, that's where I find SlowTravel so helpful. If several reviews have been posted on the ST site regarding VRBO listings, or other owner-direct listings and they're positive reviews of course, then that's also a "safer bet".