Checkerpatrol.com used to do trailer checks long ago. Unaware of any others that do them.
Certified pays less, but their data entry requires less info and software is less cumbersome than that of TNSMI-TES who pays much better and has checkers permanently assigned to theaters on a weekly basis.
BUT... their recent audience flow shops for a major soda provider were a super pain to complete and are unrealistic as it relates to accurately counting patrons coming and going from an auditorium on a busy weekend night with two entrances.