Vat and website query

Hi all

I am Acca qualified but due to ill health have not worked fully for a number of years and am having 'brain freeze' regarding a particular issue.

Basically I am looking at setting up an Etsy type website ( but for a particular genre) where crafters can sell their pieces and I take a commission. Firstly, do I account for the price of the ,say, necklace as my sales figure, or just the commission on it. And secondly, how does vat work if say I am not vat registered but the crafter is, or vice versa? Finally are there any special rules/ schemes that I should be aware of with this type of business?

Please can someone help straighten out my muddled thinking!

Thanks in advance