Avoid cheap boards that claim to have a FTDI interface as they are probably using fake FTDI chips to keep the cost down.
When buying from Ebay, use sellers that have a rating higher than 99.5%. Read the buyer feedback comments to see if there are any particular products that are problematic.
Look for high resolution photos that show:
- Bright, not dull solder joints.
- The absence of solder flux residue and solder splashes.
- Pin headers that have been soldered straight, not leaning over or misaligned from side to side (very common problem).
If what you receive looks different from the picture then file a dispute with Ebay. It's quite likely that the supplier ran out of stock from their preferred supplier and had to bring in stock from another supplier.
If you don't already have one, buy a 20x hand magnifying glass with a built in LED light. They only cost a few dollars and will allow you to spot soldering defects before you apply power and potentially fry a board. Things like solder splashes become dislodged in transit and can end up in places where they can cause trouble.
Avoid 3.3v mega328 boards that are using a 16 MHz clock as the chip isn't rated for that combination of voltage and frequency and therefore may be unreliable.