In my opinion, this kind of falls under the saying "You get what you pay for"
If someone is selling (Fixed Priced) a sterling silver item under 80% of full melt; it is either fake or they don't know what they are doing. Sellers who have actually taken the time to test every piece they list are usually not average joes; they are more often than not professional jewelers who would just melt their item before selling it under melt (and paying fees on top of it) So, a seller who is testing every piece isn't going to be selling it under melt.
Watch out for anything listed as ".925" instead of 925 or sterling. For some reason the fake silver sellers like to use that.
Watch out for stuff listed as "NEW" with Factory Photos. Actually, watch out for factory photos in general.
TBH I really don't recommend buying any item overseas that you can't just eat if it ends up being fake. In reality, the only way you can return a overseas purchase from the USA and actually be covered by buyer protection is to send it Express Mail. And this usually costs more than the return your trying to make.
If you want real sterling silver jewelry, then look to buy from a seller who is in the USA and has a 14 Day Return Policy (preferably with no restocking fee) Then you have nothing to fear.
I can't stress enough what JewelsCollecting said. If you want good silver that 99% of the time you will have no problem, then English (and European in general) silver is the way to go.
It can also be highly collectible and have much more value beyond its melt.
Do a bit of google research on Norwegian Silver, Danish Silver, Finnish Silver, English Silver, Polish Silver, etc etc.
Some of it will bring big big money, but imo its worth every penny for the quality (and peace of mind that what you've got wasn't made yesterday out of a aluminum can)
And if you want to play it safe, you should stick to designer signed items.
From constantly getting in big lots of jewelry at my husbands business; I can easily say that item's only marked 925 are more commonly fake than items signed.
I'd also watch out for items marked "925 ITALY" or "925 MADE IN ITALY" BUT not Designer Signed. Lots of these are fakes too, and the vast majority of the real italian pieces I've had are designer signed.
If you do want to buy Italian jewelry, but don't want to risk it being fake; then I recommend buying the stuff with the Official National marks (Pictoral Image of a Star ~ Numbers ~ Two Letters : like : STAR 668 FI followed by a Purity Mark)
I've yet to come across a fake piece with National Italian marks.
Another thing that could be helpful is if you are looking at something, and you are questioning its authenticity; just snap a screenshot and upload the photo of the item to the forums. Try to get a opinion from some 3rd parties who have no reason to doll the item up, and will tell you exactly whats what.
*While were randomly on this subject, watch out for 800 Silver marked "SOLINGEN"
Some counterfeiter must of got a hold of a set of old german flatware because there is now around 100 sets of this junk floating around on ebay and it is ALL fake (0% silver content)
My husband almost bought a set the other day, but he realized the numbers on some of the knife blades were "mirrored" (like 008 instead of 800) so he tested them with his Niton. Not silver at all. Would have been a HUGE loss to buy a set of flatware thats not worth a penny, and I decided to search ebay after he told me about it. Its all over the place.
So definitely felt this information should be spread.