a review on Modway furniture...  

How do you know the leg was wrong from the factory? Could have been swapped lots of places along the line so I'm not surprised they don't think its their fault. Are you saying they won't sell you a leg, or they won't send you one for free? You can fix it yourself for free with a saw and a file.

The longer leg most likely belongs on the front, with the back legs being shorter. Which means there is probably a chair out there with one leg shorter than the other three.

-The chair was a 'one off' from the seller. Its a seller on eBay that does clearance and overstock sales. The chair was a random item for them so its not likely it got switched with another chair. I'm willing to pay for another leg (although I shouldn't have to) I'm not asking for it to be free. And yes I can saw it down, but I really don't have the tools or skills to get that nice rounded bottom and I shouldn't have to cut up a brand new item to work it work!
-It may be that it needs two that are longer, either way, sitting in it 'as is' is not possible!

Clearance and overstock is what the retailer can't sell (unsalable) and can't send back to the manufacturer because its been opened or modified. Retailers sell this damaged stock cheap to a third party - this is the guy you bought it from. When he listed it for sale he should have noted its damaged condition - and it sounds like he didn't - so he is the only one who is responsible to make it right. You could have returned it but were happy to keep it by accepting a partial refund. It seems to me that when you accept that deal that is where any responsibility ends.
I really don't see why the manufacturer would have any responsibility to make it perfect. Now it is too bad that they don't have a leg they can sell you - but this is probably made in China and shipped by the container load in sealed boxes. So there are no spare legs to send you, even if they wanted to.
I guess that's one of the problem with buying cheaply made reproduction furniture - it is pretty much disposable once it gets to its destination.

Clearance and overstock very often also means b-stock and returns.
You're not going to get great customer service from a company that sells inexpensive import mass market knockoff furniture, they will just direct you to back to the retailer. Customer service is supposed to be provided by the retailer, which you bypassed in favor of a deep discount from a clearance house. Such sales are typically "as-is", with an expectation of possible defects.
So while you are not really at fault, per se, and though it's admittedly not particularly generous to say so, you get to pay the "THE STUPID TAX" this time. Everybody pays it now and then. And since the seller has offered to adjust the price, aren't you really just getting what you paid for?
Live and learn.

I recall having an elderly great aunt that had one leg slightly longer than the other(s). She was lazy. So sorry that this happened to you Grendel. Perhaps you have a friend with some tools?..or a sharp tooth? or you could install herman miller glides on 3 of 'em. Or?
Drinks are on me,
Aunt Mark

Edited- Its hot, I'm grumpy.
Mark, lets go have a Tom Collins...

That sounds good. Bring your legs. My tab.
Best,
Aunt Mark

Objectworship, what a useful expression. I've paid the Stupid Tax more often than I care to think about - more in my future, probably ....

Grendel, what a sucky situation. Besides the length, the leg appears to be the same as the others. Are you able to take it to a local woodworker to have it shortened?

Make your cut on the back end of the leg. Do you have a drill? Like a corded drill? Treat the threaded end of the long leg as if it were a bit and tighten down on it as tight as you can. Flip the drill into reverse and it should unscrew from the leg. Measure how much you want to take off and slowly saw it off... draw a line all the way around and turn the leg as you saw to be sure it is square. Get a drill bit that fits the hole and drill it out slightly deeper. Put the threaded piece back in the drill, tighten it firmly, and then screw it back into the hole until the threads sit flush.

You can document the process and then post it to their Facebook wall, if they have one, as a helpful guide to anybody else who may have a similar situation. If you want.

A safer way to unscrew hangar bolts is to thread two nuts onto the bolt. Then grip the bottom one (the one closest to the leg) with a wrench or pliers and unscrew it.
This way you do not risk damaging the threads at all.

Thanks, spanky. I used to do the dome nut method for screwing in hanger bolts, but had to resort to pliers on threads if I needed to take them out, as the dome nut would simply unscrew itself. The double nut technique makes a lot more sense, including gripping the outer nut for screwing the hanger bolt in.
This is a keeper.