Sales people, assuming commission is a large portion of their compensation as is common, are the absolute easiest to measure -"Show me your w2 form from your last job".
What if the person had a compensation package which paid really well for selling a product which could be sold by over promising? Their W2 would look awesome but the company would be screwed. I would be most cautious of business people leaving a job with a strong w2. Also it is important to see relative performance. What if they are making 100k and their coworkers are bringing home 500k? Are they still good then?
