Character mistake: Barney claims he would be losing $3478 on the real estate deal not going through. Considering the houses only were selling for that amount or less there is no way he was making that amount of money on 5% commission.
Suggested correction: I have no idea where you got the idea the houses were being sold for less than $4K. In the beginning Barney says Andy could get $24,000 for his house and $27,500 for the Williams' house (which is also how he got the figure that Andy can get into the Williams' house for $3,500, that's not the price of the house). Those 2 houses alone are $51,500 and 5% would be $2575, and he was losing out on 2 more houses.