you can shoot for the moon (30-50% net margins) but the reality is, competitors will get the deal, especially now that inventory is so low.
the question should be, how much $ do YOU wanna make? and you really need to know your numbers.
here's one for ya you probably don't know; if you are marketing to 1st time homebuyers, you will have to give them a closing cost credit of anywhere from $1k-$5k. guess what? that comes straight outta your pocket; so does the $350 survey (at least in my area), the attorney fee, obviously, real estate commissions.
another big surprise people find is building depts. making you do stuff to code; "you opened a wall? now you have to update everything.
you probably won't include your personal credit card interest as part of your costs (you should).
you also need to include your time? so how much are you making per hour?
for me, personally, the loan flip I did, after all the costs above and beyond considered, I made a 13% NET (not gross margin which can be skewed depending upon your rehab budget) and made $19k before taxes.
too many newbs have no idea on their costs in this biz.