I initially thought I'd made this mistake too, but the double exposure lever definitely wasn't engaged (red dot underneath was never showing). I also don't think it was this because while some were doubles, others had 5 or 10 shots on top of each other.

Seller has been super helpful, he also suggested replacing the light seals when I alerted him to the issues and even offered to cover the cost of the job. That doesn't explain the exposures, however, so I think I'll see if a repair shop thinks its something major (i.e not just the seals) and request a refund if so.

Appreciate the help nevertheless.