I used to use SS a lot with some very mixed results. One of the last times I did, I prepaid the reservation on line and specifically did not include a tip which I preferred to do based on the quality of the service and also do in cash when I leave the van.
I get in the van at home and the driver hands me a charge slip to sign. A credit card charge slip. The implication was that I would not get to the airport if I did not sign it (the full fare RT had already posted to my CC account) Why, and how, did this driver get my card info for an unauthorized charge? Extortion to get a tip. OK. Two can play this game. I signed it and contested the charge later and reported the driver.
I can't count how many times I used to get in the van and the driver asks where I was going and for how long? Why is that any business of yours? Scanning for potentially empty houses for a given period of time or just being friendly?