" ... Some companies I know often sell firewire cables that are made of lower grade metals and have little or no data protection. ..."
All too true. There are also companies making FireWire 400 cables that are longer than the specifications and performance criteria allow. If you see any FireWire (or HDMI) cable longer than 10 meters, avoid it as all that this does is slow FireWire down (usually from FW400 down to FW100 speeds). This is not good for either video or audio or data transfer as packets do get lost and handshaking in some data transfer modes is spotty at best.
It is our experience that there are only three or four cable makers that do it right and do it to the 1394 Trade Association and IEEE 1394 a&b specs. (A mercenary announcement: We distribute
for two of these manufacturers.)
As for material of the cable wire and connectors, a very good argument can be made for gold plated connectors, especially for professional audio use, as this does knock some of the FireWire power supply noise off of the circuit. The FireWire 400 and up "carrier" signal is up into the microwave range, so deviations in the actual wire from specs almost always produces poor or completely non-op results.
(The same applies to HDMI, really. The video signal on the HDMI wires is also in the microwave range. Again, gold plating on the connectors helps the audio side by knocking a nominal amount off of the power supply wires.)
Techies love this stuff = an "eye" image of a high quality FireWire signal: