Sounds like a reasonable offer.
You're trying to fix a problem but they feel the printer is working within specification. If it is, they're accepting that you're not happy with that specification and offering to refund you (such buy backs are typically for the full purchase price, at least here in Australia that's how it would work - that's based on the underlying legislation concerning such things).
If you don't want to send it back, you can continue to use it and wait to see if something changes.
I don't think it's a case of not wanting you as a customer, I think it's a case of them being honest and saying, "your printer appears to be working correctly, but we accept you don't agree or aren't satisfied with how it's working, so we're offering you a refund if you want it". That's pretty much as good as it gets in terms of customer service. If they can't fix the problem, it doesn't matter how much you and they want to, so the alternative is to offer your money back.
At this point, it might be worthwhile crystalising exactly what your concerns are - really drill down to the core issue that you have - and then present that to them and ask whether it's worth waiting to see if something can be changed or resolved. At this point, it's possible that you've presented so many issues to them so frequently that your real, core concerns have been misunderstood.
Again, I doubt they no longer wish to have you as a customer, (unless you've made unreasonable threats of legal action or you're rude or something like that, no evidence of which I've seen in these forums from you, so I can't imagine that's the case), they just believe that they can't satisfy you as a customer at the moment and have done the reasonable thing of offering a refund. I think you have an opportunity to clarify exactly where things stand and then either wait and continue to work or get a refund or perhaps push for (another?) replacement printer.
