Gutted!

I randomly bought this 1977 Honeywell 1250mm lens on eBay.
I was curious and I thought it was worth a hundred quid punt.
It came with the original receipt (£406 after discount which equates to about 2.5k in today’s money).
I was concerned that pictures I took with it of the moon looked pretty soft.
I took the front corrector (lens) off and inspect it. Someone had obviously smashed the original and replaced it with a piece of flat glass. That doesn’t work. Seller gave me a full refund.
Still gutted though.