I prefer the retailers that help shape the products/services I buy.
I couldn't find the exact definition that "shape" can be interpreted as "assemble". In the example above, what does "shape" mean? Does "shape" mean to come up with what to buy?
Shape is used here in the sense of formulate, design, refine, facilitate rather than assemble.
It has more to do with envisaging and planning than actually putting things together.
Assembly is the final stage of production. Shaping is part of the process that leads to it.
https://www.macmillandictionary.com/dictionary/british/shape_2