THIS! I had a friend i was living with ask me and a bunch of others to help install his garden fence (i was renting there so i agreed) carrying 30 6 foot fence posts up and 50ft staircase up to the house was hell, made worse by "your not doing it quick enough"! But i was told i could pocket the favour. Then another friend asked me and a bunch of others to help lay his foundations for his extension (again no pay, just promise of a "returned" favour) and then had him yelling at us the whole time we're weren't doing it good enough (fucking hire some actual workers then!)
I only bring these up as i never got those return favours, when i moved further into London they all had settled down and chose not to continue my friendship as i "don't drink, so its hard to socialise with you"...yep
Moral is, only do favours for those who are 100% people you trust/like, and even then don't let them take the piss!