Until you said he sent her proof of purchase, etc, i was on the side of ‘maybe not a scammer,’ but once you said that, the alarm bells started ringing again.

Dont trust this person. His story is likely fabricated and tailored to pull at your mums heart strings. He is manipulating her. What you need is picture evidence of who this person is. Or better a video call. That will prove he is at least who he has described himself as.