Purchases from a private person supplier

We have answered the question in a video: https://vimeo.com/1071779912

Thank you very much, that clarifies a lot. However, in most cases, these private persons are located abroad, and unfortunately, I would not be able to obtain their signatures or personal details. I suppose this makes it a lot more complicated. For example, is it possible to choose not to deduct these costs from my taxes? And if there is a correct way to do this, how do I go about it? Thank you in advance!

You are always free to choose not to include costs in your accounts! So it is certainly possible and permissible not to include these purchases in your accounts. Of course, you will then have more profit and pay more taxes. But that is how it is if you cannot properly substantiate these costs.

But it still seems possible to me to compile a proof of purchase with those foreign private persons. In other words, I think it's worth your while to at least try to get them to make it okay!

Okay, that's clear. Thank you!