Differential taxation - purchases at flea markets
I am currently setting up an online shop for used LP/CD/DVD. I source my goods exclusively from private individuals, so I have opted for the differential taxation scheme for tax purposes. Since the purchases are only for small amounts (usually up to 100 EUR), I will use the total amount calculation (sales minus purchases) to determine the value-added tax.
I make about 30% of my purchases at flea markets, where no receipts are issued. When asked for receipts, people just look at you "stupidly" and attempts to get signatures or names/addresses always fail.
Would the tax office accept it if I write self-made receipts for this purpose (flea market address, date, items purchased, and price/item)? Or is this not allowed for 30% of the purchases?