Advertisement prices are based on cryptocurrency exchange rates. The exchange rates are volatile and may change rapidly. AgoraDesk updates its exchange rates and advertisement prices every twelve minutes. Prices shown in the listings and on the front page are cached, and update a little slower. Sometimes when the price is fluctuating rapidly, advertisements with the same price formula may display different prices. Sometimes market data is not available for some currencies, which leads to delays updating the advertisement prices. However, when you open up the advertisement page itself the price will be more up to date. The price is determined when the trade request is sent.