Question: What are the laws about buying things (clothes, etc) during the 3 weeks. Is there any distinction between buying and wearing? What about if something is on an amazing sale does that make a difference or is it not in the spirit of the 3 weeks?
Answer: The Mishna Berura writes that any new clothing that does not require a bracha of Shehechiyanu may be purchased and worn during the three weeks. Today this includes the vast majority of purchases. During the nine days, even these should be avoided.
An item that does require Shehechiyanu should be avoided the entire Three Weeks. However, if it is marked down significantly it may be purchased on condition that it needs alterations or is not fully paid for, so Shehechiyanu will not be recited.