I knew you'd chime in here, and I knew you'd say this... ;)
I've adopted the methodology that the less time you spend in a pattern, the lesser chance that you'll end up having to share it... and unless there's good reason to not (crowded pattern; about to be crowded pattern (two or more people announcing inbound intentions still a few miles out)..
No matter how you do it... most important is to piece together a mental image based on position reports, and visual confirmations.. even asking someone to re-report.. just to be sure... and then making a decision (and accurately reporting your position/intentions).
I'd forgotten to mention the "minimal time in the pattern" thing; it is an important part of my decision-making process when arriving.
And of course, the Big Picture includes aircraft near the pattern area, whether arriving or departing; if I hear but don't see someone out there, I'll also make numerous inquiries/reports.
But I am not happy if I don't see them... you can't trust some of these folks, like the Bo driver who called "three miles", no entry intentions specified, then appeared less than a minute later, dropping
onto the base leg from above TPA, right in front of me!! :o >:( I've gotten more and more in the habit of glancing at the runway only a few times when entering and flying the pattern, looking outside 95% of the time... not the other way around!
Funny thing about that: in FS9, the AI traffic tends to fly wide patterns, and of course they ignore your position reports and can't be interrogated for updates... but at least they tend to fly predictable, courteous entries!