Someone recommended online proxy checker https://proxy-checker.net/en/ when I complained about constantly buying bad proxies, and it completely changed how I work. Now I can instantly see the level of anonymity, GEO accuracy, and speed for every proxy. I recently bought some “German” proxies, and the checker quickly showed that half were actually Dutch. That let me go back to the provider and demand replacements. I can’t imagine using proxies without checking them here first.