It all depends on who exactly restored the device. If you purchase a manufacturer-remanufactured MacBook through a dedicated website, you get a quality device at a discounted price with a standard warranty. Defective parts are replaced, a new battery is installed, the wizards completely clean the device and reinstall the software, and assign a new serial number. The device practically does not differ from the usual one, except for a more pleasant price.
When you purchase a used device, you essentially get a pig in a poke - even full diagnostics at a service center cannot give you a full guarantee that, for example, a processor or video card will not fail in a week or a month. Of course, buying it from your hands will probably cost you much cheaper, but a possible repair can cost you half a new MacBook.
If you nevertheless decide to purchase a MacBook from your hands, check as many of its functions as possible and do not be lazy to spend an hour or two for diagnostics at a service center, an hour of time is much cheaper than expensive repairs of a broken device, and if you agreed in advance to spend enough time for checking, a conscientious seller is unlikely to refuse you a quick and free check of the device.
Before buying, I also thought about this issue for a very long time, decided to buy a new one, who knows how it was restored, and after what time it may break down again.
It is important that the poppy is remanufactured by apple itself and not by some third party from China. Apple has the lowest cost for a remanufactured poppy of $ 1000, about the same price as used, depending on the model and the period of its use. Therefore, there is already a matter of choice and taste. And so I recommend a new normal macbook air 2017, they now cost 67k, that is, the same as the restored one