1825 Sovereign Bare Head Evaluation

Pre-Victorian gold isn't that common but I suspect that this one wouldn't be worth heaps due its condition (I'd say gF-aVF), but I 'm not sure. Probably more than just its gold content though.
The St George reverse variety is the rarer 1825 sovereign.

The color looks a bit off but I am assuming it's just your photos. If genuine the coin should weigh 7.99 grams and would grade around VF-35 to EF-40. I have some concerns about the rim and denticles though and have a feeling your coin may not be genuine. You might want to submit this one to a TPG for grading and authentication.
Here are photos of a VF-30 piece for sale by a European dealer. He has it priced at 900 Euros.

I strongly believe the coin to be legitimate and in relatively high grade, however, you are 100 % right on the weird surfaces, the collector from whom I bought it seemed to like playing with acids, the surface is badly cleaned and lacks the usual lustre expected for a coin which, as you rightly say lacks surface damage.
(do look at the ear though, there's a big, though quite undisturbing ding.)

I thought it looked a bit suspicious too but couldn't see any obvious problem besides the surface.