No Bullying....Simply ask if he is happy with everything that was done, the duplicate inspections done, and the paperwork finished, and the aircraft ready for the Air Test. With an affirmative response to all that.....look them in the eye and say...."Load Up!". Then have them go along with you as you do a real Pre-Flight Check....opening up access panels and shining your flashlight into all the dark cubby holes where things can hide. Looking at every Control Linkage Bolt and Nut....Cotter Pins....as you can after maintenance is a very good habit to get into. If two sets of eyes are good....three are better!
Anything but a cheerful and willing affirmative response and heading off the aircraft.....the aircraft stays parked until Management takes corrective action.
I have found all sorts of surprises on/in aircraft that were "All set to go!". From Torque Wrenches, rolls of locking wire, hand tools, rags, buckets, even a full sized damn Quilt on one.
If you find something on your Pre-Flight....write up an Incident Report....no matter how loud the whining is....and no matter who is doing the whining. You aren't being unfair.....just putting some integrity back into the system.
Engineers can kill you.....a very tiny percentage are dangerous and the vast majority are very darn dedicated Professionals trying to doing the job right....but they are human and thus able to make mistakes even though doing their very best not to. The key is sorting out that small minority that need to be in some other employment and not showing them the least bit of leeway.
I have seen some Engineers do some incredibly good work in arduous conditions and still admire them for their ability and skill. Some I would only carry a loaded gun in my hand if they were near me as they proved themselves quite happy to kill me with their Spanners.