How do you handle partial returns and support with Avalara?

[KP_Enterprises]

Are there any Avalara users who would be willing to share their experience with that App? I am particularly interested in knowing how you deal with taxes on partial returns and on Avalara's support.
It's my understanding that Avalara does not compute sales tax on partial returns and this would need to be done manually. We have a large volume of sales and as a result, a large number of returns. Is tracking this difficult?

Avalara is also slow to respond to our emails. Is this true of their tech support also?