I know they won't put a lot of thought into installation

So why put all that thought into how to do it? Buy them a rod and you're done. Would I want to reach over my head everytime I put a shirt in the closet? Don't think so!

In the rear they can put rods for out of season hanging, and then use the front for the daily stuff.

OR have a roll-out rack like this.

http://www.walmart.com/ip/Rolling-Adjustable-Garment-Rack/5995116

Would a 1.5" PVC front to back into flanges hold clothing that length (6 feet)?

It would need at least two and probably three support brackets along the way.

Steel or wood closet rod from the Borg will be much less likely to sag than PVC. We did the high/low setup and it works great. Reaching slightly upward hasn't been a hardship, getting to the lower rod is less convenient, but my stuff isn't hung there.

1" galvanized pipe makes a nice sturdy closet rod. 1 1/2" is getting pretty heavy for long runs, OD is about 1 3/4"
Casey

If the house is old enough, they will be dealing with plaster walls, so that's another thing to take into consideration.

Can you find out if there is trim/molding/a flat piece of wood running along the closet walls at about closet rod height? If there is, the closet most likely had standard coat hooks, the ones with one large and one small hook, on the molding. Clothes would have been hung on hangers and two to three hangers per hook.

The best way to use this space is not the easiest. But I'll give you some ideas and you can go from there.

First, I'd put up a closet shelf along all three walls, slightly above head height, so things can be stored on the shelf, but those entering the closet won't bump their heads.

Then, along the 30" back wall, I'd put a double rod, for hanging shirts and pants that are folded over a hanger. That will give about 58-59" of hanging space,

Next, along one long wall, I'd install valet rods, preferably the ones that swing to one side, to make getting to the back of the closet easier. If those aren't possible, I'd get the ones that fold down. You'd need at least one that would allow for full-length hanging clothes, but the other could be doubled up, just like the rods at the far end. That would give you at least 5 valet rods, with about 9-10" of hanging space on each or at least 40" more of hanging space. If there is molding on the wall, the valet rods should be attached to it. If there isn't, I'd install that first.

Then, on the opposite long wall, I'd put a bunch of clothes hooks for things that get used a lot but don't need hangers--robes, hoodies, jackets, scarves, belts, anything else that can hang from a hook. You'd have at least 4 feet of space to work with, so they could have a lot of hooks along that wall.

Under the row of valet rods, you could put a row of baskets or a low shelf for shoes.

This would maximize use of the length of the space while still allowing enough room down the center of the closet to get to the stuff hanging on the back wall.