in order to purchase an antique tea , you should be familiar with production concepts, packaging and sales ( when was sold to where etc. ) , import / export history over that decade, knowing the approximate market prices of such an antique in area / country u r buying it from ( knowing the local economy would be handy for that ) . That would help you to eliminate the obvious "fakes" . In order to get closer, you will need to in detail examine the wrapper and tea leafs it self. Close look , touch the paper ( to feel if not new ) , smell the leafs and of course / preferably to try the tea. For that you should be familiar with the storage and transformation / maturing taste in particular area/s or the places where the tea is claimed being stored in those all years. So u can actually compare what u drink with something what you have drunk ( legit one ) before. Does it make sense?
So if you do not posses this kind of skill package, you are ending up to rely on some reputable vendors.
In this case is very up to you ,
based on what criteria you select which vendor is trustworthy and which not.
To me, I can not rely on any recommendation from internet because I have never met people who recommend some shops so I don't know their level of knowledge about certain product ( in this case old tea ) , yet never bothered to browse a history of individuals in order to kind of know them. There are some people who are dedicated to old tea , vendors who are on FB groups. You might try to post the picture there and it's easier to browse trough the history of each individual to see how deep the his/hers knowledge is ( yet not 100% , coz many knowledgeable people do not post much ). But I believe it will help a bit to understand the persons background a bit.
If want to hear my personal opinion, I'm very skeptical to teas below 2000y which appearing on internet. Those kinda teas , at least in China, being usually sold offline or via wechat groups between trusted people. Now, don't take it as status quo. Things might be different in Mal, TW,HK.
Please note , that's only my very personal attitude : I'm not a person who on something because everybody on internet says so
In past few years , being in tea biz, I see how that kinda believe / trust is being abused. There are some vendors who can get way with ridiculous claims just because they've built their reputation in the past, and now just drifting on the Chinese tea marketing concepts without filtering out those "fakes" since it is either too much hassle ( requires upgraded knowledge with developing tea market, time and failure sometimes ) or probably coz it sells better than real , more expensive stuff ( people like expensive tea for cheap ) .
As suggested here before, buy sample , if like the taste and thing it worth your hard earned money,then go for it. NO point to focus on Legit / Not Legit , if you are not a collector with skill set mentioned above.
have fun, and share with us the taste of that one, if u purchase it.