Looks like no return policy:
Dear Zachary,
This email confirms that you have purchased a 1-Year subscription to iTunes Match for $24.99 on 11/14/11. This subscription will automatically renew each year unless you turn it off no later than 24 hours before the end of your current subscription period. To cancel the automatic renewal of this subscription, sign in to iTunes with your Apple ID and go to your Account Information page.
Regards,
The iTunes Store team
Odd, I have also read that there is a 30-day cancellation policy on this on another post over at Apple's forums. You'd probably have to call and ask, and the person on the phone may not even know the policy.
To answer another post, that same post says you have the 20 (or was it 25K?) limit *on top* of whatever you bought from iTunes.
Also my observations based on last night's iCloud session:
I have about 100 or so "ineligible for match" songs. These are scattered throughout the library. So I have one CD I ripped, and of all the tracks, one song on it (Don't Fear the Reaper) is listed as ineligible. There were ripped at 190k too.
There's also a collection of "error" icons as well. No explanation for them, but they refuse to be added even though a few of them are well-known tracks.
All my metadata was preserved.
Also, you can use Smart Playlists to sort how iTunes handled your match status and identify which were matched, which were uploaded, which were purchased, and which were ineligible.