Actually yeah....it makes it worth less on the market since it reads Martin. Doesn't matter if it's the same exact horns as one which is engraved Yanagisawa. This is why it is relatively cheap.
Seller could not have sold it (private sale) at the market price of a Yani-engraved T880.
From a sax-curiosity point of view, it may be collectible to an extent. But not from a monetary value one.
He might be able to get a bit more (+/- 250pounds) than he is asking, however. So jump on it, if he guarantees it plays well.