I had a new 710 frameset back then and it had the Reynolds stickers on frame and fork. A buddy had a 510 (I later got one used) and it had the Ishiwata 022 stickers on frame and fork. None of the Treks I assembled or sold back then had tubing stickers they should not have had. The seller is misinformed, blowing smoke, or ignorant; you decide which. If you want the bike that's not a bad price but be aware of what you're actually getting.
My 510:
