That people can simply agree that the value of a "coin" can only go up is completely asinine, and identifies TBC as a scam even before several other factors are considered. The following is taken from the info section of the TBC website.

The Billion Coin Membership Agreement
The formula begins with a membership agreement. All members of The Billion Coin community agree that this coin will never go down in value; it can only go up in price. This agreement is hinged on a software program that drives the price of TBC up by 1% to 5% daily until it reaches its Ultimate Price.