If something is on sale in a supermarket (for example, 3 for $5) and I only want to buy one, is it true that they have to sell it to me for the price I would have paid per item if I purchased 3 (so in this case would they have to charge me $1.67 if I bought one)?

Yes that is correct, there is no need to buy the 3 items.

Depends. Sometimes you CAN be required to buy all 3 to get the discount. It's usually in the fine print.

Depends. Sometimes you CAN be required to buy all 3 to get the discount. It's usually in the fine print.Well I've never experienced that in any supermarket in three provinces.

They do it in the US, generally you do get the piece price, though in the case of an uneven division they may charge the higher piece. For example 3 for $5, doesn't divide equally. Its 1.666666 So they might charge you $1.67 each if you buy less than 3.