If you're in a business relationship, put it in writing -- don't rely on a handshake. A $15,000,000 claim against Navajo painter R.C. Gorman's estate was recently dismissed. An individual claimed he was owed half of Gorman's 30 million dollar estate due to their partnership. Another independent source had indicated the claimant had done "background work" for Gorman. Gorman's will had left the claimant $10,000.
Handshakes are tough to prove, especially in a probate dispute. When there is no writing to support your side of the story, you're generally going to have to make a very strong case to prevail. If you find yourself without a writing, sometimes seeking a compromise with the estate (on moral or some other grounds) may be best. An estate compromise agreement may allow you to enter into a settlement with the estate, but these documents, negotiations and reaching agreement can prove challenging from legal, tax, emotional and many other areas. Timing can also be very important.