It’s often a very slow leak as I understand it, so signs can be subtle-
That said, he should’ve been able to take a satisfactory photo/ video with the car up on a ramp.
Exactly the same with my tyres- he’d drawn big yellow marks around what he said were cuts.
It was extremely suspicious the way he only very briefly focused on the “ cuts”, so I couldn’t actually see them on the video.
I had it booked for MOT with them too ( and they were telling me the tyres were a fail) - I told them to take the yellow marks off and not do the mot.
I got it through the mot elsewhere the following day, with no problem at all.