I typed a full comment but it just didn't load. Oops.
I've been in a similar situation to you OP and I'm with you 100%
My DS is on a team, a boy on the team lives a few streets from us and his mum's car got written off last summer so she asked if I could give him a lift to and from training once. I didn't mind at all.
She then promised the favour would be returned once she got a new car and started asking me regularly, it became a weekly thing to training THEN it also became a weekly thing to tournaments but for the tournament's I was taking the boy, his mum and the older sibling.
A few months passed and I asked if she'd found a car yet and her response was "no, I've decided I won't be getting another car because I've saved so much money by not having one as other people take the kids to all of their clubs, and to school, and I get a lift once a week to do my weekly shop with a neighbour. So I don't need a car and it's just a waste of money." 
The boy and my DS weren't friends. Me and the mum weren't friends. We just happened to live close-by.
The boy then started joining holiday clubs that my DS was doing because they knew he had a free lift. One day, my son didn't go to the holiday club as he started puking very last minute, so I messaged the mum to tell her and I was still expected to give the boy a lift - I did, because I felt guilty that it was so last minute but she then asked me to go back to pick him up at the end of the day!! I said no to that! CF!
My other son has just started other committments at the same time as training so I won't be driving to training from home or returning home after the session which was a perfect excuse to get out of it.
It started as a friendly favour, but after over a year and no thanks I have 100% completely had enough. The boy is so cheeky in the car, swears like a trooper and is so disrespectful; plus it made me feel so tied - I couldn't just nip to the shop or stop by to visit family as we passed on route or on the way home.
Totally different circumstances, but a similar situation with a CF mother. Whatever you do, be careful. Ha!