So far in my yarn buying experience I've turned up very little yukky yarn. The little I have was ordered through the web, so I couldn't touch or see it. Instead of returning it, what I've done is use it with other yarns.
For instance I got a green worsted yarn that had no life. I tried knitting, I tried crochet, and it just wasn't happening. Then I tried a strand of brown with flecks of orange in it along with the green, and it was very appealing.
Another yarn was just screaming loud, yellow orange with greens and reds in it. I've put together a scarf with long rows, alternating the screamer with a compatible red, and it's handsome after all.