I had something similar but babysitting not a lift
I used to be a massive people pleaser (not anymore!) and one of the mums at work mentioned she was struggling for someone to have her youngest while she worked one Monday
I offered as I had the day off and she accepted-no money changed hands and she dropped him off/picked him up
Somehow,within a month,I was walking 2 miles to pick him up from our work every monday/tuesday(she told our boss not to put me down for monday/tuesday shifts),going home,feeding him (which cost me a fortune),walking the 3 miles to her house,picking up his brother,waiting for his siblings to come home,cooking their dinner and then dad would walk in,no 'thank you' just grunts and I'd walk home again (all unpaid,not even covering the cost of feeding them/nappies/wipes etc)
More than once she dumped all 4 on my doorstep in the holidays/she was going on a night out
I'd had enough and told her to sort herself out-id offered as a one off,not every week until they'd left home
She went nuclear-slagged me off to every single person we knew-about 3/4 (who had been telling me I was a mug) turned on me,vague fb stauses and caused endless problems at work and our boss (who's arse she'd been kissing for months) tried to haul me in for a warning (I said I'd take legal action if he tried and he did back off while looking for any excuse he could find to give me a warning)
She also tried to tell everyone I'd tried to lure her husband into bed but he'd turned me down-that was a big fat lie (thankfully my dp believed me)
It caused so much stress,i almost had a breakdown-her childcare had become my problem and I was in the wrong for not sorting it out for her (dad was one of those where childcare was 'a womans' job and he'd only have them for half an hour or so until she walked in)
I'll never babysit again unless it's for my dgd or my very dear friends dc (who i adore)
Looking back,I'm amazed at how i was sucked in but she knew what she was doing from the first time of having him
I'll never be that mug again-its a firm 'no' unless I want to do it