Documentation

There is not any standard set of documents which can be vouched for sale & purchase.

I don't know whether you have done any control testing in context of sales or purchase cycles.

Another thing is the controls set for manufacturing Co & retail co are different. Hence if you have done control testing it will be easier for you to decide what documents you need to choose, from where you should selcet samples.

The general documents\areas in context of Purchases:-

1. Material Requistion, 2. Purchase Order, 3. GRN, 4. Quality Check Approval, 5. Supporting for entry in Stores Register, 5. Payment Details

The general documents\areas in context of Sales:-

1. Sales Order received. 2, Invoice, 3. Entry in Outward register, 4. Receipt of Payment

Please note that this is most general list I have given. It's Very theoritical in nature. To answer your question, details regarding entity's procedures in context of purchase & sals is necessary.