It’s important to be realistic about what you can check beforehand. Most proxy companies don’t offer IP samples before purchase, so initial testing usually happens after you get access.
For static or dedicated proxies, using tools like Pixelscan, IPFighter, Whoer, or IPQualityScore can give you a good idea of IP reputation, location accuracy, and fingerprint behavior. It’s also useful to test them in a clean browser profile to see how they perform in real conditions.
With rotating proxies, though, checking a single IP doesn’t mean much since you’re working with a full pool. In that case, it’s more about the overall network quality and consistency over time rather than one-off checks.