Back to the OP's post....
"I watched the person mount the scope"....
If you are going to shoot LR, you need to learn to mount your own optics, not being a smart ***, just being frank.
Levels are cheap and tabletop gun vises like a Tipton are as well.
I'd never trust anyone to mount a scope when it's so easy to do correctly yourself.
It's assuredly canted and the rifle/scope together are probably canted when shooting, a common issue.
The scope cross hairs must be at a right angle to the axis of the firearm and must be in the same relationship when the round is touched off.
To a smaller extent, scope misalignment can cause compounded errors. Did the person lap and align the rings in relationship to the base/rail, prior to mounting the scope? No rings or scope, no matter what they cost, are any better than the mounting job.
Anytime you see a scope for sale, anywhere and the seller states... "ring marks', you can rest assured that the seller didn't lap and align the rings, prior to installing the scope. Severe ring marks are a good sign that the internal mechanism of the scope may be damaged.
Finally, if the rings are in alignment and properly lapped, the ring to tube contact is at it's fullest and when the caps are installed and the fasteners torqued to specification, the scope will never slip in the rings, due to recoil.
Finally, I'd add a scope level. Len has them in his LRH store on this site btw.