Use personas. If you recruit using personas that have been developed based on customer research then there can be no issue that you have brought in the right test participants, because you can use the attributes as screening criteria.
Allow enough time and double-check. Make sure you allow for enough time to ensure you are getting the right people in. Have two conversations… One to initially recruit and a second follow-up conversation just before the testing. The second conversation is to ensure they were being genuine in thier initial responses. You may find that some recruits lie to get the extra money.
Recruit extra participants to have as backups. Don’t just get 10 if that’s what the research calls for… Get 12. That way if there are last-minute no-shows you don’t have to scramble… Much.