Buying new is no guarantee that it won't have issues, and getting warranty service is a time consuming PITA. Buying used adds the element of "grading" to the mix. Reputable resalers not only stand behind the products they sell, but the grade they apply to the equipment. Over the years I've bought quite a bit of preowned stuff, never had a problem with it.
In addition to
KEH,
B&H,
Adorama, Roberts Camera,
MPB and Samy's Camera all sell preowned, open box and display models. Because of their grading system and guarantee they will be higher priced.
EBay is cheaper, if there's a record of return policy with the seller it can sometimes be a place to look. FB Marketplace is somewhere you roll the dice, maybe your lucky, maybe you aren't, the price reflects the gamble.