The process of refurbishing products can be somewhat complicated. What you could do is consider a number of factors ranging from quality control to safety testing.
The first and most important step in the refurbishing process is to ensure that the product being sold to you is of good quality. The process of testing and certifying products starts with the company whose product you are buying and proceeds to a 3rd party company called an independent testing laboratory (also known as a 3rd party tester or just tester). The tester will look at the product from a mechanical standpoint (e.g. is the product well made, easy to use, etc) as well as from an electrical standpoint (e.g. are the plugs and switches safe and easy to use, do they work as intended, etc). This independent testing could be helpful for larger priced products. For cheaper products, it could be useful to just look at the reviews of the seller of the refurbished products. If a deal looks too good to be true, it probably is.
Repairs & Replacement
Another important aspect of the refurbishing process is to ensure that the product being sold to you can be easily fixed or replaced if it breaks down. The easiest and most popular way for customers to show their discontent with a product is to let others know that they are having trouble with it. So if a customer buys a Microsoft Surface and within a month starts having problems with it (e.g. it stops working consistently, gets damaged easily, etc), they can bring it back and have it fixed or replaced by Microsoft. The same goes for any other type of product that is widely used (e.g. laptops, cell phones, etc).
Overall, buying refurbished products can be a great way to save money while still getting quality products because the companies that sell them have already gone through the process of quality control and safety testing. But you must be careful not to buy a product that was damaged during testing because in that case, there might be no way for the company to provide you with any type of warranty. Compare Refurbished Products in the United Kingdom.