That opens a pile of other issues. For reference, when I showed up at the ER it was a Canadian hospital. They called the surgeon in early, for me. I think word went out that they were spinning up an OR early and the ultrasound tech rushed in. So cost and turnover weren't really an issue. Everyone was salary, the equipment owned, and nobody standing to profit by cutting into me without need. Frankly, everyone had a good laugh at how quickly the system came together. But I did fall into that category of people who showing up on evenings weekends that, statistically, don't do as well.
Its extremely hard to definitively define best practises. You'd be surprised how many practitioners still argue for what look like clearly outdated ways of doing things. There's also the argument that in some people's hands an outdated way of doing things is safer than a newer (better?) way of doing things in their hands. eg. A surgeon who has been practising for 30 years but only recently learned to use a laparoscope.
I doubt ambulance chasers do anything other than muddy the waters and enrich themselves at the healthcare systems expense.
Old school surgeons will insist that they can reliably make the diagnosis without imaging (and that's probably where you get a 20% false positive from). Some institutions will push this notion too - either to reduce imaging expenditure or increase surgical turnover (sad but true).