What country is the rifle from? Isn't a name I've seen on a double rifle before. I assume it's Edwin Wilson. There were two that I can find, Birmingham and Norwich. No listing for an E. Wilson in London.

If it is British, small shops rarely actually made double rifles, so it was probably bought in from the trade. If that's the case quality will have to stand on it's own.

If it's British, it's easy to tell Nitro Express vs BPE. Just ask for photos of the flats and water table. Be aware, especially with this caliber, that Nitro Proof can actually be Black Powder Express (Nitro for Black), not Nitro Express. Make sure you understand the proof marks before you jump.