We used USA Transfers last time, I reserved a van for 4-7 people for $65 (we were meeting another couple at the airport). As it turned out the other couple brought along yet another couple (for a total of 6 people) USA Transfers refused to take the final couple because they "were not on the list". After going back an forth for a while, and delaying out arrival at TTR, the other two couples ended up getting a ride thru another company and we went alone to TTR yet were still charged the full $65 (I still have my confirmation and receipt) THEN, on the return back to the airport they wanted to pick us up over 4 hrs before our flight time, which is totally not necessary. I spoke with a cabbie right outside TTR, got a ride to the airport for $20, picked us up 1 to 1.5 hrs before flight time, he took us the back way thru town, took only 15-20 mins, and had no issues making out flight. I don't know if this is the exception or rule with USA ?? So not everyone has had a positive experience with USA Transfers !!
I can't speak to the previous post of having more people as we have only ever been two but I can speak to the return times. If you want a "closer" return time, just ask. They will not guarantee that you make your flight on time if you ask for anything under 3 hours but they have no problem honoring your request. On a side note, we have had flights where we check in and walk right through security only to wait at the gate forever. We have also had flights where we have waited over 2 hours just to check our bags. We were already formulating plans in line for what to do when we missed our flight on the worst one. You just never know what situation you will walk into at the airport.
In the past we have booked USA Transfers for a 4-7 person van with other couples coming with us, they have never asked for the names of the other couples just my name which was the only name on the booking and confirmation form. In their on-line booking form they do ask for the number of people in your party, perhaps that's what confused them. You probably only specified 4 and then showed up with 6 .... a call to their office when this happened would probably have cleared it up since their drivers do strictly go by what the booking/confirmation form states.
We used Aventour the last time because it was free shuttle provided by the resort. They were absolutely awesome.
Actually, USA Transfers does take prepayments on line. Used them in October and paid 2 months earlier. Can't say enough about their service. The drivers are polite, friendly and always on time. You don't have to ask if they'll stop somewhere for you, they offer that!
As per detailed on the booking confirmation, I once add people to my transfer back to the airport and let them know 1 day in advance before 6pm, and had no problem, no extra charge. I didn't have to give names only number of total passengers travelling.