The country of origin has no effect on the people you get. If your population is 8% housewives you will get 80,000 housewives when you buy 1 million people.
When you sell population you sell only young workers.
Maybe they would like to help another player by paying over the odds, also happens the other way round. Because its quicker too. And, not everyone feels inclined to give their GC to the GM.
I need to sell from my slave and you need to sell from your slave. If we both bid 10 coins no one will out bid us. The transaction will go through when the bid time ends whether or not we both log in before the end of bidding.