Mine were in fine shape aside from one of the fuse covers being broken. This is obviously a non-issue. If I were you, I'd take it up with the seller. I hate to think I referred you to someone bad. On the plus side, inverters are not generally a show piece and if they were, you'd send them out to get chromed anyway
In all seriousness, email the seller and ask for an explanation....
As for hooking them up...to test them I just used the 8 gauge wire and clamps that came with it because I had a small load. However, the inverter is likely to draw close to 90 amps at full load and 8 gauge really is not sufficient for this IMHO. On top of that, the clamps are only rated for 50 amps, but are the factory unit.....go figure. My plan is to run a similar setup to car audio systems. I will run a 1/0 supply line from the battery up to a distribution block in the inverter compartment and then run a 4 gauge power lead to each inverter. Grounded will be done in a similar method. While chassis grounding is more ideal in some situations, I think in a high load setting like this with the batteries not running things like an ECU and in a well ventilated placement, I think running a ground directly to them like a person would in other high draw situations such as a plow or winch on a truck.
The way these will tap into my 120 lines in the bus is rather simple and hardly elegant. It certainly is not the most user friendly method or erhaps safest, but is more than sufficient for my needs and the price is right.
I will run a 20 amp supply from the outside of the bus to 3 (6 plugs total) GFCI outlets. The outside supply could be hooked to shore power, a genset, etc. These outlets will be in my inverter compartment. All the circuits from the bus (6 total for lights, outlets, etc) will have simple plugs on the end of them with labels. This way I can plug in all of the circuits to the inverters or the shore power supply or any combination of the two that I feel is necessary. As I am the only person who will likely ever have their hands in this compartment I'm not too worried about it. I know the GFCI outlets will do little to protect against overload, but there won't be an overload situation in the bus other than perhaps a short in which case the GFCI will of course trip. When plugged into the inverters there will be no breaker persay on the circuit, but the inverter will shut down at a roughly 7 amp load due to overloading making it hardly an issue.
I wish I could be more descriptive. Any comments on this layout will be appreciated