wiltingfast- welcome!
I get samples from many sources, but one of them is a good seller on eBay who sells multiples of the same for very few pounds. I often find that ordering 6 of the same off them means I have some little mixed collections I can give to friends or sell.
It's a curious fact but if you buy some mixed samples on eBay it seems to cost a lot more. I've seen four mixed samples go for nearly ten quid, but you can buy say, 12 Cartier samples for around 7.99. (You can always sell them on with other samples once you have them).
So you can, in theory buy six, use one, sell five.
I also find that if you take out a points card in the Perfume Shop, they seem to be more generous with samples, but usually only if you buy something.(I even got a Chanel 2ml sample!)
Also, its worth remembering that half used, ancient bottle of perfume will usually sell on eBay! Lots of perfumistas I know are often swooping down on their prey this way. Something dusty from Nan's wardrobe could be vintage Diorella. You get the picture.