Are you suggesting that every source uses the same manufacturer, or that every manufacturer uses the same exact raws and the same exact process? This is just silly. There are so many variables that determine how good a manufactured product/drug ends up being it's ridiculous to say, "if it says it's Anadrol then it's exactly the same as the Anadrol made by every manufacturer in the world.", which is what your suggesting.
If we were talking about pharma grade drugs then you might have a point, but we aren't -even with pharma there can be variables that make a difference. We aren't talking pharma medicine, we are talking about underground labs in China. BIG difference, my friend. And, big difference in the quality of many sources.
I mean, by your logic we don't need to shop around for a source whose gear works best. We'd just need to hit the cheapest price list because it's all the same.