I use two booking sites for my condo and here is the difference: VRBO customers are difficult. I'm not sure how VRBO does their marketing, but almost every single potential customer has done one of two things: they've asked me a lot of questions about aspects of my place that are listed on the site already (they're too lazy to read the entire listing) or they've tried to negotiate the price down. Often they will do both. I am frequently asked to charge a weekly (and lower) rate for stays of 3 to 4 days.
I am a hard-working home-owner who keeps a very high standard on the rental condo I have listed with VRBO. I've had to deal with potential customers like those described above and then with people who make sarcastic comments when they see I charge more in the high season (to offset the low season so I can pay my mortgage).
I think VRBO must be the place where customers feel they can get a bargain. It's too bad because that has led to some troll-like behaviour. I am sticking with the other booking company. I don't need the headaches of VRBO customers.