OOP means "out of print". Some sellers will take this to mean that the fabric is worth a large sum of money. It may be a fabric that is hard to find but highly sought after. Just for giggles, do an eBay search for Heather Ross fabrics. These are long OOP and some sell for $50/yard or even $10+/FQ.
There should be no reason not to use OOP fabrics unless the cost is prohibitive.