safe-guard yourself against fraud and scamming. 
Use only vendors that you know have legitimate credentials.
Here are some things you can do to establish the legitimacy of your musician(s).

1. In the case of musicians, you can check to see if they are in the local musicians' union membership.
2. Ask for referrals from previous customers. Speak to previous customers. Ask them if they were happy with the music and if the musician(s) was professional, courteous, punctual.
3. Check their alma mater(s) to see if they attended and/or graduated with the degrees they claim to have. You'll find mine; New England Conservatory of Music and Yale University, on my bio page.