I don't usally enjoy using the buy and trade aspect of this, but enjoy more the selling. Since I uasally play a Industrious civ and have democracy and eventually get replacable parts I have really fast workers and get annoyed with slower slave worker so I sell them to another civ and get some cash after a war is over. Also if I want to buy them put in a city I can't get them to trade for many times, and rival workers in my city, which results in foerign nationals could screw me in later if the other country is next to me and out culters me. In short I like selling the workers I gain during war but, not buy from other countries.
There is only one instance in which I would buy workers, that is when the worker is actually mine (either if it was lost in war or I sold if for some odd reason)!! Those ar my thoughts on the subject but not the your only answer, I thought it would be best if I had told you my thoughts incase they sound good to you (if they do I hope you know there are rules a using drugs in America).
Thanks for your time!