Allow me to say that I had worst lenses that are now in mint condition, all you need is an experienced repair guy, for once you should be happy if you hear noise when shaking the lens, this means a loose screw or a problem with lens barrel very easy to fix.
if you have the skills to repair lenses this can be an easy job
my 100 macro got worst than that, it had a tiny screw missing, repairs time 15 minutes, cost 20$
my EFS 17-55 had that to a lesser extent : needed just calibration, he replaced the rear mount with a special rear mount (found only at Canon repairs not sold on the market) using live view projected to TV he played with a few and screws till the image of the chart he was shooting became sharp with clear edges. He told me before live view they used a mount that projected a chart via the lens to a wall (or screen )same adjustments were made till image became sharp, total time to repair 30 minutes, cost 40$
A friend's 10-18 was totally decentered sent to repairs: one of the screws on the lens barrel was misplaced, repaired in ten minutes, total cost 20$.
Maybe I am lucky to have a good repairs guy close by.
I would suggest if the guy accepts to give it a try and attempt repair usually with such a severe decentering the problem should be quite obvious and easy to repair.
What I do before buying such gear: I tell seller I am ok to pay that price for the lens repaired, he takes it there either he repairs and keeps when he finds his lens is good again, or I buy it in mint condition with three months repair warranty.
That's how I got efs 10-18 fir a friend for 180$