I booked a rental through Autoslash, paid for it and showed up at the Avis the car was booked at.
There were hidden fees that weren't mentioned by Autoslash and Avis wouldn't let me get the car unless I paid them. I was at the Avis desk when I called Autoslash and Autoslash said to just pay them, send the receipt and I would get refunded.
Did as I was told, sent the receipt and they said I would get my refund. Waited a week and heard nothing, upon following up they told me they decided to deny the refund and they would not help me further.
In the end I have to chargeback my card and file with the state attorney general. It would have been cheaper and easier to just book directly through the car rental company.