Vintage and alterations

I'm interested to hear your thoughts about the following situation: you're at the thrift store or vintage store. You see an item that you really love and you try it on, but it's too big or too long. I'm not talking about buying an item that is extra large when you're a size small, but say pants that are slightly too big at the waist or a maxi skirt that is very maxi on you if you're short. Do you: buy the item and alter it to your waist size / shorten it, or do you leave it behind for someone else that will look better in it as is, even if you really love it? I know people have opinions about altering vintage and I'm curious to know what you guys think.