I may have posted this before, but for those people saying when CFs give you a lot less than you give them for birthdays, etc, why don't you just give them less - this was my experience of doing just that:
A couple among my in-laws (call them X) always sent tokens for birthdays & Christmas, & DH sent them tokens in return. It's not what my family did, so I left him to get on with it, thinking it was daft just to exchange the same amount of money.
Then I realised that while DH was sending them £20 per person in tokens every time, they always sent us £10 per person! This annoyed me, because we were just starting out while they were older, had higher salaries & owned their home (& seemed grabby in other ways, too).
After a little (ahem!) persuasion from me, DH sent them £10 per person. All was now equitable, I thought. Until our birthdays came round, & X sent us £5 per person!
So X fell into the category of 'CFs who know exactly what they're doing'.
A second example, from my family:
A person stopped sending cards when she got engaged, no idea why. As she was younger than me, I carried on with cards etc. She always sent us free e-cards. This went on for a long time, until I wondered if perhaps I was embarrassing her by sending cards when she didn't, or whether they were unwelcome. Perhaps she'd prefer that I did what she did, I thought. So on her next birthday I, too, sent a free e-card. My birthday after that, she sent me 'Happy birthday' written in an email - not even a free e-card!
Some people just feel they're owed, & the world is out of kilter unless they get back more than they give. No idea why.