Hi Denis,
I've been doing lease purchases for many years and I've never asked a buyer to put down 10%. If they had that kind of money they can get a loan and purchase it right there and then. I usually ask for 1-2% down on the lower priced homes and in the bigger, more expensive homes I ask 3-4%. Of course nothing is written in stone. There are many variables in the process that will effect the amount both parties will agree on. However, one main thing to keep in mind, whatever the amount, DO NOT SIGN for something you're not sure you can pull through. If you can't close by the agreed upon date, you will lose the money. So, be careful!