I buy lots of little electronics modules form eBay, very rarely if ever have an issue with them and they're almost always cheaper than I can even buy the parts, let alone spend the time to lay out and have a board made.
It makes it really simple and quick for me to try new chips (MPU-6050 IMU at the moment for a Quad Copter project), use utility parts (nice little TDA2030 amplifier modules or LM2596 SMPSU chips for instance) so I've got boxes of handy little boards I can grab when I need a bubblegum circuit to test something.
Last year I bought one of those little breadboard power supplies, looked like a great idea except it didn't fit my breadboard so it got consigned to the bits box, cheap enough not to worry about but too good to throw away, handy DC socket, two regulators (5V and 3.3V).
Today I needed a 3.3V regulator and just couldn't find one so I desoldered the regulator from that PSU* module, rigged it into the circuit I'm working on and...
SMOKE!!!
The damn thing is either faulty or fake and passes the full input voltage to the output pin (and yes, I got the pinout right), it's short circuit.
Tested the 5V regulator too, that's also short.
Lesson learned, test first and that particular board is in the bin after destroying a nice little Frontier Silicon DAB module.