Parlay advice

Parlay advice I've got a local that thinks he's big time. He's been around for a while taking $50 and $100 bets from people that just bet the favorite and the home team. He stopped by my shop today with some parlay cards. Some of the lines are stale and he doesn't know enough to change them or cancel them. He thinks I'm a mark, so he was basically trolling for my business. Even though parlays are normally a bad bet, if you are taking 4 or 5 teams and keying a line that is off 3 or 4 points with the possibility of getting paid 20-1, does that make the parlay worth it? I'm thinking this....I take a 5 team college card using favorable lines for $50 every week and the same with a pro card. When I've lost $1500 or so, I up it to $100. Eventually, I hit and get my money back and drop back to $50. Of course, this is based on me having an advantage that a couple lines are going to be off by a field goal or more and a couple of others may be off by a point or two. I don't need to retire on his money. Just make a couple thousand every year or so till he kicks the bucket or I do. Is this realistic?
Here's what to do. Find the best line that you could get down at. Go to [url]https://www.sbrforum.com/betting-tools/half-point-calculator.aspx[/url]. Next, use the table in that link to buy half points until your line matches the one on the parlay card. Next, multiply the individual bets together and see whether it pays worse than the parlay card would. If it does, the parlay card is +EV relative to if you'd bet those games individually.
Just because a line is off by 3-4 points doesn't make it an automatic winner. Remember that 83% of the time the line means nothing. Either the favorite covers or the dog wins outright. 17% of the time the fave wins but doesn't cover.
This is what I played this week. I meant to do a card for college and pro, but I got to it too late. Maybe an all pro card tomorrow if one of my college games lose. Rice +10 Duke +13 Uconn +5 Det +8 Balt -10 $50 at 20-1