Nothing is authenticated. No item passes through Metzee's hands, and there is no verification badge on a listing. What does Metzee actually do about fakes?
What you have instead is a seller holding the object on camera, which is more than a photograph gives you — if you use it.
The five checks
1. Ask for the label, close up and held still. Stitching, font, spacing, the way it is attached. On almost every category the label is where a fake is weakest, and a seller confident in an item will hold it steady.
2. Ask what came with it. Box, papers, receipt, dust bag, certificate. Not proof — a fake can come with a fake box — but a seller who has them says so immediately and a seller who has none should say that too. What is provenance?
3. Ask how it reached them. A straight answer is normal. A long confident story with nothing checkable in it is colour, not evidence.
4. If it is graded, check the serial while they hold it. Every major grader has a public database. A seller who will not hold the slab still for ten seconds has answered you. What is professional grading?
5. Ask what the worst thing about it is. The question that tells you most about the seller, in any category.
The red flags
Catalogue or manufacturer photographs on a second-hand item. The clearest one on this site. Can I use the manufacturer's photo?
A price far below what the real thing goes for. Not always a fake. Always a reason to ask more.
The words. Replica, first copy, master copy, dupe, AAA quality, mirror image, OG quality. Those are not allowed and the listing should not be there at all. Can I sell a replica if I say it is a replica?
Refusing to show something specific that would be easy to show.
What the format gives you that a listing cannot
A photograph is chosen. A request is not. Asking a seller to turn a thing over, under light, in real time is hard to fake and takes ten seconds. How to judge an item through a camera
What protects you if you get it wrong
A counterfeit is not as described. Raise it within 7 days of delivery, whatever the store's returns policy says, and report the store separately — your refund and their conduct are two different outcomes. What happens to a reported seller?
For the expensive categories
Buy from stores with a record, start small with a new one, and accept that waiting is a legitimate choice nobody should talk you out of. Should I bid with a seller who has no sales yet?
More: Metzee's position on counterfeits, five questions worth asking before you bid, how to find a seller you trust.