Flat rate, depending on mileage to site and duration of trapping program. 1 week for small properties with minimal activity. 2 weeks for larger properties (or smaller areas with very heavy activity). Set heavy on initial set-up. Hammer them quick. First check in a day or two, then checks spaced out depending on activity. I have the duration, then 4 different rates depending on mileage to site. Took me 15 years to figure out what works (for me) on mole pricing. As Jim stated.... takes the same amount of gas and time whether I catch one mole per trip or 10.
Did a job about 8 years ago for a guy in a high-end lake shore subdivision. There was a company from 40 miles away (St. Louis) working the area (neighboring properties) charging $100 per mole... no set-up fees or trip fees. This was 10 miles from home, and on a route I drive constantly. Gave him my pricing info (which also includes info on mole biology) and he hired me instantly. Back then it was about $300 for a 2 week program at that distance from home. It was a 3-acre lawn, which I think they cut by hand with a scissors (just kidding, maybe). He had spent a couple grand over a 3 year period on grub control (Tru-Green) with ZERO reduction in mole damage (of course). I caught 21 moles in the first 3 days. That would have been $2100 from the STL company. Word spread fast about my service, and I now take care of 90% of all the lakefront properties there.
Second mole call of the year today. Snow just melted off the lawn, and the lady freaked out. I think this mole was using a GPS, judging by that rectangular pattern.
Caught the first one about 3 minutes after setting. She was thrilled. (The lady, not the mole!)