You can't do a damn thing if the airplane can't fly and that's up to you. A lot of 135 operators using outside vendors are not vetting/auditing them prior to allowing them to "work" on your airplane. I understand the struggle of being at some weird out station far away from your base and having someone miraculously show up to bang some things with their fixing sticks and sign off your required paperwork. You, as the PIC, can ask dispatch to verify with maintenance if the vendor is on the approved vendor list. That list is required by the FAA and the procedure your company is required to follow before they work on your plane is explained in the GMM. Some people will just try to keep moving the jet regardless, it happens. Pick your battles, nowhere is perfect. But once you sign the paperwork you're legally and civilly liable.
