transmission went bad and he just put some Lucas transmission fluid and it was a temporary fix. My question is how can I tell if someone puts Lucas into their transmission because its gone bad?

 

You can't.

 

Why did he put Lucas in the transmission in the first place? Going for a Hail Mary on a faulty trans?

You really can't tell unless it does not smell like ATF. Most ATFs smell the same and look similar. And even then you would probably only notice slight differences when the fluid was new, not after its been put into a trans.

If he wants to give it a shot try flushing the trans, maybe try something like Type F and see if that brings it back to life.