I see. Even if you are using a dollar weighted average, with no limit on interest rates, you can create strange situations. Let's look at an example:

$50,000 lent total.
$49500 lent at 60% per year.
$500 lent at 88,888% per year.

Dollar weighted average: 948.28%

So, even a small 1% loan at a high interest rate can modify the average by more than 10x. There is possibility for market manipulation here.

You might want to find the standard deviation and throw out all the outliers. So, you could calculate only using a 95% interval. You throw out the top 2.5% and bottom 2.5% loan volume and calculate the average using the remaining 95% loan volume. At a current $50,000 loan volume that would require someone to borrow more than $1250 at a crazy high or crazy low rate in order to affect the market.