#1: Your pricing is at the worst possible point on the curve. You charge ten times more than what the inveterate cheapskates want to pay. You charge ten times less what a
middling domain name is worth. You are opting to do business with a lot of "pathological clients" this way -- they will want the moon and stars because you cost TEN TIMES MORE than GoDaddy. (There will be, inevitably, comments in this thread to that effect. Do you want to wake up to a mailbox of them every day?)
#2: Let's talk inventory. It will cost you, for the sake of argument, $10 to hold a domain for a year. That means, to break even, you need to sell one out of every ten you register. Since you're going to be dealing in 3 word domains primarily, that is going to be a bit of a stretch. Let's say you branch into bingo for a day and start thinking up domains -- you can count to 500 just by starting with Xbingocards.com and filling in topics for X. Are you going to be able to unload 50+ of those?
#3: You need to do a heck of a lot of manual gruntwork here. Presumably you'll automate the actual purchasing, but you'll have to think up hundreds or thousands of domains and then sift down to the ones which are actually salable.
(If you doubt this, I will give you a list of 500 Xbingocards.com domains and you can time how long it takes you to winnow it down to as narrow a field as you think is winnowable. My guess is just the filtering would take most SEOs I know upwards of two to four hours to do if they did it systematically. And then, of the 46 or so you end up with, will you actually be able to sell them?)
Do this poorly and you'll be out money. You'll find that you're eventually spending a lot of money and effort to buy yourself a retail job, if that.