As others have said, if a potential buyer is making your hairs stand on end, go with your gut, avoid the hassle and block them.
If you feel like redoing any photos maybe try natural light on a white windowcil - or on a piece of white paper on a window cil.
To improve focus on the chain, work out your cameras focal range - probably 20cm minimum if using a mobile, get a sturdy box/ stack of books of at least that height and prop your camera/ mobile on them to have a really steady and sharper shot. Click focus on the element you want sharp, like the hallmark and clasp.
Check that the hallmark listed as a UK hallmark, is a UK hallmark - assayed at one of the UK assay offices (so anchor, castle, lion or rose stamp alongside the metal fineness). Most made in Italy chains I come accross are supplied hallmarked, with Italian hallmarks - now perfectly legitimate to sell in the UK.
Weight always goes down well on gold listings if you've got any scales that go down to grams.
Have you considered adding special delivery postage as an option - might speed up the sale and you could set as buyer pays.
