I'm an old user of Gmail since 2004 and I rarely have checked spam label in search of false positive spam emails.
Do you have some strategy/technique to find good emails or you just browse the spam label and check them one after one?
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Just browse the spam and check; you'll get the hang of it pretty fast. Normal emails usually don't have many numbers and strange characters like % or UPPER CASE PRIZES etc. in the message preview, so you can actually browse very quickly.
What I guess you're looking for is an automated way to do this, which would actually be a spam filter.