I recently had to hang ikea cabinets in a basement that had metal studs 30 inches on center. The Ikea cabinets is approximately 50 lbs each and it is a three piece set. I used the Ikea rack system.
I used 8 ez drywall anchors with 75 lbs threshold across the ikea rack over 60 inches. Within that 60 inches were three metal studs which were tapped into using #8 cabinet screws.

Would this arrangement work? Should I be worried? I went into this not expecting the metals studs and not 30 inches on center.

I would be concerned, at least in my own house. I'm only in my 30's and the amount of weight in one of the cabinets in my own house makes me wonder how well I attached the IKEA rail. My wife has enough plates for an army, and there's just two of us. My point is, that one cabinet in my house probably has 200lbs of plates, bowls, cups and what not, because it is all part of a set, and she wants them together. Right next to it is a cabinet that probably has 10lbs max full of spices and seasonings. You shouldn't think that 8 wall toggles at 75lbs each will be okay, because the cabinet on the end might be where they put all of the weight. The weight will never be evenly distrubuted.

I think when you run into that kind of situation where you expected one kind of site condition and ended up with another, you need to learn to charge a change order, or not install the cabinets. You don't have to be a jerk about the change order, just explain that the wall is not safe enough to hang cabinets on and this is why.

Here are three ways I would fix it. Easiest case is that you have to cut out a 4" strip of drywall and replace with 1/2" or 5/8" thick plywood depending on the drywall thickness. A good piece of hardwood scrap would be better.

It would be better to sister a wooden 2x4 to each metal stud. You should be able to sneak in a 24" 2x4, then rotate it and secure it to the metal stud, even putting in a couple through the face of the drywall. (See illustration I attached) You could then reattach the drywall piece you removed and patch the drywall, if required. Or put a piece of plywood or hardwood across the hole as mentioned in option 1.

The most difficult would be if the wall is an exterior wall and you have to lug a hammer drill down and stack some 2x4's (i would use treated one the first one) to the foundation wall and build out to the correct wall depth. This isn't my favorite, but it should work as well. I would even angle my tap cons a few degrees in each direction to help with pull out.

All three of these would probably work fine, and are better than what you have. The first option might still be on the weak side, but I don't know your exact site conditions. Are they light gauge studs? 30" On center framing doesn't really make sense, to I would probably want to error on the side of caution.

All of these options should probably take less than 4 hours, even if you had to run to the hardware store and grab a 2x4, and then run home to get a hammer drill. I would just charge them your hourly rate for 4 hours, or if you have the scrap and tools already in your truck you could probably do this in 1 to 2 hours and go easy on the homeowner. They probably didn't build the wall and are learning about their house as well.

Hope this helps, but doing it right will make you sleep better at night.

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If you screwed into the metal studs across the top and bottom of the cabinet back and have the drywall anchors or toggles there should be no problem. I have hung cabinets only on metal studs.