This reminds me of the clients who ask why I charge $5 flat rate S&H on all print orders. "Hey, that's pretty steep to mail a 4x6!". Yeah, but it takes me about the same amount of time to put one print in a photo mailer as ten.
$8 to fix a chain is nothing, I would expect that to be their minimum "get out of bed" fee. Sure it would be a nice guesture to fix it for free, but most retial stores can't pay the rent on nice gestures.