Yep, I absolutely do and I see no reason to be ashamed of it. I have never listed an 18 yo player of mine at that time of the season but I do not blame people who take advantage. That's the nature of competitiveness.
I believe most managers don't even take this "opportunity" into account when listing their players, they probably just want to sell them early to get fresh funds for the new draftees. As to the "tricking" part - no-one's forcing anyone to buy, it's actually quite simple to make sure of the age of the player in a number of ways before you bid.
Yet, I do recognize the issue and how it could be troublesome, especially for not so experienced managers and I actually suggested possible solutions.
Cheers
BBB: 2 (S37 S38); Top tier: 7 (S35 S36 S37 S38 S39 S41 S63); Cup: 9 (S25 S35 S36 S37 S38 S39 S40 S41 S61)