Mindark, as the creators of Entropia Universe, (http://www.entropiauniverse.com/), have created a very decent game that uses real money in game, but they allow free play where you can work for money by collecting "vibrant sweat"

now the problem as it stands now is there are not enough use for this item, and as such, the market is flooded it the extent where no one really buys it. The price for sweat is between 1-2 ped per 1k sweat, (that takes about 4 hours to get) so it have a value of about $0.10 to $0.20 for 4 hours of work

As there is a chronical surplus in supply and little use for it, and thus little demand then it happens that people spend hours, or days gathering this sweat and end up realizing that nobody is buying it. this cause people to give up on it and on the game, and they end up just quitting.

so this is how to fix it:

1. add vibrant sweat as an ingredient for every blueprint,
2. link the amount of sweat to the value of the item at a rate of 1 sweat for every 10 pec of expected item value

• items under 10 pec don't need sweat
• items valued 1 ped will need 10 sweat per attempt
• items valued 10 ped will need 100 sweat per attempt.
• and so on and so on..

This will give sweat a use, and revive the lower end of the economy, the added price of the sweat on production will just be passed on to the final consumer. paying a slightly higher MU.

crafters will then have a choice of either buying sweat or sweating themselves, so they do not need to spend extra money if they don't have to.

Mindark will benefit too, as fewer people will quit the game early on,  it is mostly startups that sweat.