Most 12 string guitars I ever had in hands did suffer from bad fine-tuning.

Here some things to think about:

1. Tune it down. Dab Savage is completely right, 12string guitars should be tuned down at least one halfstep, depending on guitar type. Ovation 1/2 step is enough.

2.Strings. Use the lightest strings available. The best for 12 string guitars are THOMASTIK PLECTRUM AC211  .11-.50. YOu will not believe that it is your old guitar when you try them.

3. Setup.String action and neck relief should be carefully watched. The best string height on the 12th fret is 2,25mm +/- 0,25mm. This is the measure from the fret surface to the string.If you have an Ovation and you have no shims left you will need a neck-reset, (but this is really no big thing when you have a post-1980 USA model with bolt-on neck).

A guitar neck must not be abolutely straight, the strings need space to move, thus a very little bow in the neck is better.

Most 12string guitars have poorly made nuts and saddles. The nut should be made so that if the string has contact with the 2nd fret it should be a only avery tiny space between string and 1st fret ( a thin stamp).See pic1

The strings on the saddle should have precise positions. I saw so often that the strings were "somehow" positioned on this. It makes playing so much easier. see pic2

Many if not all 12string guitars have a too wide string spacing on the nut. Playing will be easier when you have the strings pairs a little narrower. Unfortunately you will have to replace the nut, but this is no great business and will give you more playing comfort for years. see pic3

If you have done all this perfectly your guitar will not be the same. But it takes a little more precision and patience than on a 6 string guitar. I have done these modifications on all my 12 stringers over the years and all of them are very easy to play.

Maybe you find here some ideas to even make better! Good luck with your guitar. 12strings are best!!!