If you allow for sales then I think it goes against the grain of the competition which is an "investment competition" and the very essence is to remain in a particular counter for the longer term rather than trying to turn this competition into a trading operation. If the tide turns because of a broad pull back chances are that it will affect all investors in the competition across the board. If one looks at the shares chosen by investors some have tried to pick penny shares with a view to making significant gains - but this is only likely to happen over the short term - so its a case of - you pays your money and you reap what you sow. If you do allow sales then maybe you should restrict it to only one sale a month - this could create an admin nightmare for yourself, and similar fees must be imposed as for buying of shares
My thinking was either one of two things, a) only allow selling at a loss (ie avoid the tax-man's definition of trading), or b) running two parallel leaderboards. One for traders and one for investors. If someone sells at profit they are automatically marked as a trader.
There's still a few months to iron this out so I'm sure we'll find something that works. My goal with this website was an education into investment, so I really didn't want it to be a trading contest. I feel investment is something South Africans don't think about enough, and even more so when it comes to equity investment, the best performing class.