Mining Contract Questions

[alan929]

Trying to find mining contracts that are a win/win situation.
Purchased a few on eBay and always got 50-60% of the btc I would have gotten if I would have purchased from coin base.
Why would anyone sell a mining contract if they could mine the btc themselves.
Thinking that just purchasing the btc is the best way to accumulate.
Any suggestions? 
Thanks in advance.