For instance, my brother in law was figuring out which cover to use for a part of a product its company was about to produce.
He then asked me and my sister to be "guinea pigs".
He asked me to feel 3 sticks covered with different materials, we will call them stick A, B and C.
So he first asked me to pick the material I preferred from stick A and B. I was confused because they felt kind of the same, but I did pick A. Then, he introduced stick C and asked me the same. The touch and feel for me was better with A, smooth and even, so I staid with A.
He then asked my sister what she preferred between B and C, to what she answered "C" with no hesitation, and added "you want a good grip from wheelbarrow handles, and this one feels it won't slip or anything like it".
Interesting, isn't it?
Would I have picked this one as I had known the purpose of the cover - to be on the handle on wheelbarrows? Stick A and B were actually the same, no wonder why I doubted myself!
If your guinea pig don't know what he is testing for and looking for, it's hard to tell what would be the best, but then, sometimes, we need "blind" tests.
Treat answers you get with caution, knowing that sometimes your questions were not given in a good context and the person giving them to you is not your target customer.