I know someone who is a good poker player, plays a conservative game.

If i were to bankroll him in a no limit game, what percentage would be fair if he wins. I mean should it be 50/50 , 60/40 in my favor. Any thoughts would be appreacited.

First of all, don't bankroll him for a one off session. When you do stuff like this it is to his advantage to take risks. Because if he wins he gets half of the winnings and if he loses he loses nothing.

So if you plan on bankrolling someone it needs to be a long term deal that lasts typically at least 18 months. This is to protect you that he needs to be playing winning long term poker and also covers the fact that if he wins a lot of money, he cant pull out of the deal then bankroll himself with the winning he already made off your deal.

Staking (or backing) another player isn't just something you do out of the blue like Ribbo has already pointed out. There is several factors to consider with one of them being that the player will most likely build up what is called a "cake" (debt) with you which obviously needs to get paid off down the line on top of whatever share you agree on.

You also need to lay out what games you staking the player for. SnG, MTT or cash games? A typical MTT staking deal could look something like this.

You agree to stake the player to play $10 tournaments and you agree to stake him for 10 tournaments (or a given time frame). To keep the math easy I just put it on 10 tournaments. Hence your stake would be $110 and since you're a good person you settle for 50/50.

Let's say the player (horse) doesn't cash in 6 tournaments and then cashes a total of $1000 in the remaining 4 tournaments. This means that he's build up a $66 cake in the first 6 tournaments and with the 50/50 deal he would owe you 500$ + $66 cake. Of course the $66 would be then used again to continue the staking so he doesn't actually owe you that since his win covered it but the money would be used for tournament entries again.

Some people do a net 50/50 share without the cake or without a buy-back but that's -ROI for the staker unless you've got a hot horse in your stable rolling in the $'s for you on a regular basis.

The reason you need the cake paid off is that it's very possible that your horse doesn't cash for 10 tournaments in a row. Hence you're sitting on a $110 cake he has build up and you're shipping him another $110 to continue playing. He then either needs to settle his cake from his next larger cash or you'll have to adjust the share to something like 60/40 in order to recover the investment. If he then still doesn't cash you should put your horse down and get a new one.

You see that if you really want to stake a player you'll have to layout your deal down to the point either with cake or without cake. However the staked player is always at liberty to use his share of the winnings to play tournaments to himself to which you're not entitled to a share.