mostly look for hand-soldered joints, EEPROMS that are where the MASK ROMS should be, and wires.
A real cart wouldn't have a single wire in it, but when you're doing a 'cheap' run of boots, you design it as best you can, then you fix them after the fact, rather than making another run of cart like professionals usually would.
SNK did use some EPROMS (with the window) in thier carts, but most of the chips should be mask-roms. They just look like a standard black chip with little white writing on them. An EEPROM can look just about the same, as it's programmed electronically. The big give-away is when you have a 'window'(wich looks just like you'd expect a window in a chip to look) on all the chips. That means that they didn't have the money to produce in large quantity.