I'm a professional tailor. If it's made out of fabric I will tailor, alter or repair it with few exceptions. Sometimes I get minor complaints about the cost to do a project (sometimes to the point of the person not even picking up the finished work, but that's a subject for another day), because they paid less for the item than the cost to do what is required to make it usable.
But the time required, plus the cost of the thread, machine needle, wear & tear on the machine, electricity to heat up the iron to press it after I've done the requested work (or to run the steamer, in which case there's an amount for distilled water too), is the same whether your project is a pair of $300 Swiss voile sheers from Ethan Allen or a $20 pair of polyester ones from Target, or either one purchased for $6 at a thrift store.
I regret the outward 'unfairness' of that, but the way I see it the client has a choice: either an item that is unusable in the state in which it was purchased, or an item that is usable for the purpose for which it was purchased. If you didn't care whether you ever hung the curtains or wore the clothing, why would you bother to buy them in the first place?