I sold off about 3/4 of my practice to some friends, for 33% of receipts per year for three years. We presented it as a merger, and in fact still work together on some clients. We share the web site and file portal and I still field general questions (cuz people still email me first) but copy them. For more complex problems I forward to them with a note to the client that I asked X to respond 'cuz I'm out of the office today. In general it has worked really well for all of us (me, them, and clients). But 40% for four years is too much.