buy (something) off the shelf

To buy something that is ready made for purchase from available stock; to buy something that is not custom built or crafted. We use our own custom software, so we can offer much more precision than what you can buy off the shelf. If you buy a hearing aid off the shelf, it'll be less expensive, but also much less likely to help you than one prescribed by a doctor. After my grandmother inherited all that money, I doubt she ever bought anything off the shelf again.