Good points, Anil. In fact, I'd go even further. There's not only a distinction to be made between a real trench watch, i.e. one used in the trenches, and military-issue watches, but also between real military-issued watches and non-military watches with a military styling and design. And, if you want to complicate matters even further, there are watches which were bought by the War Department and engraved with military markings - but never actually issued and then sold as army surplus. Ebay is riddled with all these categories and it can be a minefield to sort through when looking for the right article.
The point that I was making is that you see lots of these "trench" watches on eBay, and part of their selling/marketing play is to cash in on the current vogue for military watches, and for WW1 timepieces and militaria in particular. Many of those advertised as such are simply not - and they're a con. This is not to say that they're not decent watches - they may well be - but they're being offered under false pretences and sometimes at inflated prices. That's why I'm so picky about what I buy - and I never buy to make money, just for the love of the item.