Listed and sold on eBay for £42 with 6 bids, this £500 catalogued item would seem a bargain?

However, looking closely at the cancellation the letters appear very oddly formed?

Enough to suggest to me this is very likely to be a forged cancel?

The incentive is clear, £170 mint, £500 used.

The inverted overprint appears genuine, the slightly offset to left of the stamp to perforation is consistant with other known genuine examples.

The Cancel Enlarged: