302 is the page google delivers for blocked IPs. It’s a 302 redirect to a CAPTCHA page.
All Scrapebox does is query google like a regular search for the word, a simple word query. If it comes back and we can see the results then the proxy passes, if it returns a redirect (302) to a captcha page, then the proxy fails.
Typically google will unban an ip in 48 hours or less. So if you let an ip set for 48 hours and its not unbanned then it may be permanently banned. Google does sometimes permanently ban some IPs, generally they ban the entire IP range.