Looking at my wardrobe it would suggest about one in five but the true ratio is much wider as many were bought blind or were gifts, so of the ones I've sampled I've gone on to buy one in thirty.
Three things about this.
1; being relatively inexperienced I find I have to really live with a scent for a long time, I can like it but do I really love it, if I love it I'll buy a second bottle.
2; some of them have been bought on reviews as reference scents, Le Troisiemme Homme and Cuiron for example.
3; the quality of samples, almost exclusively the samples I have payed for have come from Lucky Scent and the Perfumed Court, yet there have been discrepancies between samples and full bottles. For example the 5ml decant of L'eau de Navagateur while very nice, wasn't bottle worthy in my eyes, my brother loved it and bought a bottle and what a difference; stronger coffee note, better tobacco, leather and longevity. So now I've bought a bottle of my own. It does make me wonder about Eau des Isles, Bois du Turquie and Bois de Portugal, rejected after sampling but.........