I have yet to be shown where middling is profitable over the long run. Most generally if aperson is a decent capper they will have the advantage over time of getting the "best" number with the best odds, compared to buying amiddle and looking to make something. The reason middles are iffy is because there is no guarantee. You are more than likely going to lose something when you play them.
Scalp/arbitrages, a whole different animal. But also a whole different world. Basically you need to take leads these days and guess which way the line is going to move. And hope it moves enough to get you what you want.
Problem is, other than baseball,(and the overnights there are usually stunted) the limits are not high enough to make it worth while. Sure you can get 20-30 cent swings in NCAA hoops games, but with no overnight MLs and a $1000 limit when they do come out, the risk of taking a lead isn't always worth it.
But ultimately it is about volume. If you can get 4-5 games aday in bases, and a decent amount in the other sports that is what makes the difference. But once again you still need thelimits. Risking 2000 to make 20 isn't my idea of fun, especially when yo u might have to put one bet in at a place that may or may not be top notch.
I fool around with the exchanges, but they are also pretty scarey, especially when they are matching pretty much any number you throw up. There is no way in hell some of thosenumbers are matched by other players, so that tels me the place is backing them themselves. Pretty scarey when supposedly thatis the beauty of it...it is suposed to be "safer' since it matches player versu player. But I don't buy it myself. But then again I am a cynic.
But the 3 things you need are patience, money and balls. A short memory doesn't hurt either. But you can't have an ego and think you are better than the game. Just take what you can get and get out. If you want to get an ego bet the NFL, generally that will solve that problem. Although this year has been surprisingly profitable, so counter productive on the ego check, but very productive in the bonus money for the year.
The best sports for getting the most return are the sports you can't get a lot of money down on. So once again you might see some 6-7% returns simultaneously. But one is always a small book with a 200 limit so not even worth the risk.
So no real advice really. You just have to do it. Sort of like poker, you either havea feel for it or you don't. All the math and expertise isn't going to help if you can't read a guy and you get trapped for all your chips. Same as taking leads. You sometimes have to take sides you odn't like because you know they are oging to move "your" way. That is the hardest thing there is to it.
Players left to their own devices will do/take most anything!