If you want a new battery for your Dyson, buy a tool battery adapter from Amazon and buy the tool battery from your local hardware store. Same price or less and you get insane run time + a new tool battery.
This x100. The Dyson batteries are expensive and die quickly (someone mentioned their experience mitigating the failure time by waiting to put the vacuum back on the charger until after it has cooled off). Getting a Milwaukee adapter for my Dysons has worked out really well. Runtime is much better, and I have one less custom battery size to deal with in my house.
Realistically, there are probably some legit 18650s and lots of fake ones. But it could be difficult to figure out which ones are legit before buying them. Co-mingling of warehouse stock is often cited as a reason why this is impossible: a legitimate seller may list their items, and then some sellers of fakes come along and state that they are selling the same SKU, and Amazon will mix all of these in a single bin in the warehouses, and you don't know which one you're getting in your order.
Just buy it on mouser or other providers that have direct relationships the manufacturers.