There are a gazillion options when it comes to purchasing LifePO4 (or any other Lithium-based) batteries. Some (maybe even MANY) of the options are so well priced that they are too good to be true. There are certainly good deals to be had, but if a deal is too good to be true it probably is.
Why is this?
Put simply there are great differences in the quality and build of batteries. There are different grades of cells that make up the batteries and of equal importance, there are so many options of battery management systems (BMS) that are of varying quality and functionality. So in a nutshell: Cells and BMS!