My first motivation is the fun of bringing home some foreign memories and way of life. In addition, it is a culture in Igbo land (Nigeria) that a traveler doesn't report home empty handed.
The price is very important; I must assign value to the souvenir, relate the price to Naira equivalent and then balance to know if it is worthwhile. Even if not, I must fetch something home, no matter how little.
I always prefer to taste before buying in large quantities to avoid wasting resources. I hardly buy the ones I tasted that are common in my home country or that I did not like after tasting.