Sure, when buying complete circuits off ebay in a hurry this is a different story.
The problem with many ebay modules of all kinds is that while cheap, they are designed too cheaply. The goal seems to be to shove these out at $0.99 shipped skimping wherever possible, while you could often get the job right for say $1.25.
This is a problem for people starting in the laser hobby as well, as those cheaply built circuits have their problems. You can buy a tiny mystery-chip driven constant current driver off ebay for $0.99, plug it in in and hope it works.
You can also spend $2 or $3 on components, build it yourself, and figure out why it doesnt work in case it just doesnt.
I have nothing against cheap ebay stuff in case you want to build something cheaply and quickly. The downside comes when these things don't actually work and it's a pain to reverse-engineer them, whereas a proper circuit was engineered such that you can indentify any probably faults with it.
Obviously many people are not engineers and just end up with a problem, and then ask questions. One thing i'd reply to that is that it may be -very- time consuming to reverse engineer a tiny 4 layer board where the manufacturer was nice enough to scrape off the part numbers, let alone let you access the programming inside any microcontroller on them.