My ends used to get frizzy because I wasn't taking care of them and using heat regularly. Then the the "stylist" would re-relax them saying my hair had reverted. So then my ends would be *really* damaged from over-processing.
It is very important that you don't let the stylist apply relaxer to the ends!
To avoid the frizziness, be sure to baby your ends: deep condition regularly, moisturize the ends between washes, cut down on heat, etc. Also Dabur Amla Hair Oil on the ends as a pre-wash oil treatment helps to smooth ends when they seem too far gone. And as locabouthair says, the baggy method is very effective in preventing frizzy and/or split ends.
HTH