This is actually one pretty cool aspect of Bancor's price discovery algorithm: it makes pump & dump operations a lot less feasible.

See, when you make a trade with a smart token contract, the price is calculated as if you made an infinite amount of very tiny trades. With each tiny trade, the price for the next goes up slightly. So, if you try to pump or dump, the price will rise with the size of your order & you'll wind up paying a price that takes into account the amount you've bought/sold.

Therefore it'll be extremely expensive to attempt to manipulate the price via pump/dump schemes.