Edit: Since pathetic people keep downvoting this to avoid helping other people get them just save the post so you can benefit from it later, feel free to repost this guide to help other people since everyone is so keen on not helping other players, don't have to credit me just want to get it out there
Couldn't really find anyone talking about how to specifically do this and having an alpha container was getting kind of frustrating so I tried sniping containers, managed to snipe a beta and an epsilon within 5 minutes of each other just now so figured I'd share how I did it
Ok first off for anyone unaware, Fence acted as a flea market before the flea market existed, as far as I'm aware everything he sells was sold to him by actual players, fortunately you can also sell secure containers to him and people often do when they earn a kappa container or an epsilon container since they have no use for their previous one so they just sell it to Fence meaning it's available for other players to buy from him on the flea market
To do it just do this;
Go to the flea market and select secure containers, don't click the alpha container just click 'secure containers'
https://i.imgur.com/z8yVwFT.jpg You should see something like this, you see how the top alpha container is being sold by fence? the greyed out one from peacekeeper will always be there, when you refresh the page alpha containers will always appear ABOVE peacekeepers listing and all other secure containers will appear BELOW it
Put your middle finger on the F5 key, your thumb on the Y key and hover your mouse over where you think the purchase button will be if a secure container were to pop up on your next refresh
Spam F5 to refresh the listings constantly, then once you see a container appear immediately click purchase then hit Y with your thumb, this gives you the best chance of sniping one, sometimes they do take a while to appear but I've been pretty lucky with them today, seen quite a lot of gammas and epsilons
The containers themselves are kinda expensive, betas are around 600K, Epsilons are around 1.2 mil, Gammas are around 3 mil and I haven't seen a Kappa as I don't imagine people are too keen to sell them after grinding all of their quests
Proof in case you think I'm lying for whatever reason