Why would the OP offer to sell for 30 BTC if he actually thought the units would ever earn 30 BTC?
![Wink](https://bitcointalk.org/Smileys/default/wink.gif)
There can be good reasons to ask for less money.
Ask too much, find no buyer, and then you are left with whatever you make mining, let's say hypothetically 30 BTC in 9 months. However, lets say you ask for 27 BTC, find a buyer, and then move said BTC(or cash) into a better investment that makes more than 30 BTC over the same 9 months.
And there are still many risks/unknowns regarding future difficulty, hardware failure rates, market movement etc.
I say BTC in my present wallet usually trumps BTC in some future wallet
![Grin](https://bitcointalk.org/Smileys/default/grin.gif)