Developed This System, Glitches

I have developed a system that buys weakness and sell strength, i.e, buys at a limit price below the market and sell at a limit price above the above the market. My inquiry was re whether metatrader charts show last trade, bid or offer, and the response was bids. Therefore all my sell limits will be filled when the price on the chart in simulation equals my sell price, but all my buys will be filled when the low of the bar exceeds the buy price by the amount of the bid-offer spread. When I rewrote the program to reflect the above logic, the system was very profitable. Any glitches I am missing here?

Thanks,

Liz