Depends on the knife. If the knife in question was to try anew pattern or size, such as a "medium" Buck 303/373 size stockman, which I did not like in the least, or a small sunfish/elephant toenail. I'll give them away.
Some knives/patterns I'll never try: The Peanut size, for example. I already know it is too small, and I'll never carry it.
Others, like the standard two blade Trapper, It ain't oft, but I have been known to tote one about every other blue with raspberry/hot pink and green plaid moon. I'll keep 3 or 4 in the accumulation.
I have never sold a knife. I've lost/misplaced, and given away a few. And, as a youngling, there was a time or dozen I took a "Frost knife shaped object" I'd been given on a bicycle ride, or out in the canoe or row boat, and "accidentally" threw it into the Mississippi River proper from the old US HWY 136 toll bridge (as far as I could throw it downstream from the bridge) when on my bicycle ... (more than a few "Shimano" below Zebco 202 quality reels, and their junk/garbage bicycle components also went off the bridge,) or overboard in/on one of the slue's of the Mississippi River, when I was using step-pop's canoe or rowboat.