No worries.
First off, you ARE taking a shot at him. It doesn't make you at bad human being, I've done it before.
Second, There's no reason for him to cancel the on market number, he's only going to cancel the bad line. If I was that guy I'd look at it and think "Nice try asshole now you've got a $500 bet on something you don't want"
Third, I know the whole equity thing can be confusing. The first thing you need to ask are what the implied odds of it not going to a playoff. -330/+240 would imply 72.3%
So you multiply the win amount by the win percentage
1200 x .723 = 876.60
You then multiply you potential loss by how often it's expected to happen
500 x .277 = 138.50
You then subtract the two
876.60-138.50= 738.10
$38.10 more then scalping it for a guaranteed 700