Buying the 5/9

I was having an argument with someone about buying the 5 or 9 instead of placing it. I maintained that since the vig was collected up front at this casino, that it would be a bad idea in the long run, but now I'm second guessing myself. On numbers where the vig is an even 5% ($20, $40, etc) it's definitely a bad idea, but what if you really stroked it out and bought it for $39? Is there a point where buying the 5 or 9 becomes a viable strategy when vig is collected up front?

It is going to depend on where the casino rounds the vig up.

Let's assume the casino rounds the vig down (don't think this is the case though).

$40 place bet 5 would be paid $56 (7:5)

$40 Buy bet -$1 Vig = $39 Buy bet would be paid $58 (3:2 38 of bet is paid 57, the remaining 1 gets 1 so 57+1)

So, it appears you get $2 more, IF the casino rounds any amount down.
You would get $1 more, if they charged you $2 vig on the $39 Buy.

However, I think there is something about the number of times the bet is expected to lose that makes it a losing bet, but I don't know how to explain the math. I'm sure one of the gurus will explain it.

The house edge on the Place 5 is 4%. The vig is 5% house edge. I don't think you can recover that extra 1%, even with rounding down.