Well! Lots of different advice, and all good. It depends on how busy is your server with bidding wars.
I hate bidding wars.
I always consider buying my youth if they are 15T or more, if they will replace an older guy. The loophole at looking value I think only works on a few people's os's. Doesn't matter, the T youths are almost always high value, enough that if you sold them you make more than buying $.
When you sign the free one it is worth training him to see how he does, I have got a couple faster freebies and if you get them early enough they can even be worth keeping. Most often they get sold though.