I saw a certain bow for sale with only one problem. It is tillered for shooting split fingered and I shoot 3 fingers under.  How big of a deal is that?

It's not.  Most bows are tillered for split finger, and a lot of folks shoot them three under.  May have to set your nock point a little higher.  That's about it.

What does tillering 3 under achieve?

No problem, just raise the knock a bit.  Bare shaft it and adjust the knock to your shooting style.  All the bows ive bought are tillered for split finger, i just adjust the knock. You will see no difference.

Tillering for three under is nothing more that adding a little more positive tiller on the upper limb.  You will get the same result by raising your knock.

Thanks fellas