People with good boundaries tend to head fledgling CF-ery off at the pass, often without realising it. "Can you..." "Oh I am busy, sorry I can't". Many of the CF tales are often following a prolonged period of ramping up minor CF-ery that escalates over time into eye watering WTF levels of cheek. Most of them are not first 'offenses', and when asked about the friendship the poster will be like 'oh yes, they've got form'.
The best defense to CF-ery is not to accept yourself being treated in a way you yourself wouldn't treat a friend. And also a certain amount of not being gobsmacked into saying nothing. The number of stories where people don't say a word to the CF because THEY don't want to appear rude is depressing!