Here is a simple classfication of trading systems:
(Lets call it Giraffe's Classification of The Trading Systems...:rofl::rofl::rofl
1. Type A Systems: That don't work
2. Type B Systems: That work
Type A is what you will get an offer to buy. It will work sometimes (mainly in trending market), but will fail most of the time. Don't be misled by there performance in trending markets. They will rock, as will anyone with even a few months of experience in the markets.
Type B is what you will never be able to buy this easily and this cheap. These are the systems running on the computer of prop desks, institutional desks and the infamous "black boxes" on the colocated servers. They take years to program, require constant tweaking, exhaustive monitoring, sometimes requiring coding for some segment in primitive computer languages to save a few miliseconds and millions of dollars in costs to develop. Most of them are quant based and analyse every bid, every ask, and every tick. They "work" most of the time or atleast greatly aid a trader in "working". It unlikely that someone will sell there "Golden Egg Laying Hen" to you....:rofl::rofl: