I feel like a reasonable way to deal with this situation might be to look at the user agent: if two requests come from the same IP but different user agents, th

I feel like a reasonable way to deal with this situation might be to look at the user agent: if two requests come from the same IP but different user agents, then it's likely that it's either actually two completely different people (behind a NAT), or this situation the GP described. That's certainly a bit more effort to implement, though, and the author night not think it's worth the time.