Why does the shopkeeper say 要不了 (yào bùliǎo) after the customer proposes a too-low price?
'要不了' in this context simply means "can't take" (can't accept).

In English, it would be "I can't take $60 HKD (for this merchandise)"

The shopkeeper refused to take the $60 HKD in exchange of that particular merchandise

要了那六十块就要交出商品了 (if she took that $60 HKD, she would have to hand over the merchandise)