I see to it that I always sample expensive fragrances. If I immediately like the scent, it usually takes me at least two or three wearings to test the longevity. Doesn't necessarily mean that I'm going to purchase it. My main motivation for sampling is the experience.
A lot of sampling. Having access to stores with a broad selection (eg New York) is almost a necessity.
I had read the Turin Sanchez book before, so I had a list of what to sample. The first one I got almost right away, so interesting was it. But then I took the time to smell a couple of dozens at least before moving to the second purchase. And then I kept smelling more and more.
Being in Canada a lot of the times the shipping prices throw me off of ordering samples so when it comes to niches that I can't smell in person, I do a lot of research and dabble in the dangerous and exhilerating sport of blind-buying. I know why I shouldn't (and I can't really afford to hate a fragrance), but I still do it anyways.
Unless you have more money than you know what to do with, sample first. Order samples of what you are interested in and go through your sample. Once you start sampling you will most likely find multiple scents you love and want to own and you will see how expensive it would be to buy full bottles of all of them.
Another option is to buy a decant after you finish your sample if you are sure you want to own the scent. I personally recommend doing that as you are starting out, because no doubt you are going to find plenty of things you love and want to wear. I just ordered 2 decants from Surrender to Chance. One cost me $26 and the other cost me about $19. Since I am wearing a lot of different things these days as I sample, I know it will take me a long time to work through my decants. So I spent $45 on the decants, whereas a full bottle of just one of those scents would have set me back over $100 and who knows how many years it would take me to finish. For that same price I can have multiple decants to enjoy. Once I finish a decant, then it might be a sign to buy the full bottle.
I usually flit between a few stores testing or getting samples and always much more than I want to purchase on the day. When I have made my choices for the day, I already have a good idea what I will be buying on my next expedition. I don't buy blind. In desperation, one time it happened -- it was Chevalier by D'Orsay (I think all the reviews were positive on BN). I moved it on quickly though -- didn't work for me. Never buy on someone else's say-so.