Need help on Taxes and Pricing

Read some of the posts on this board.

I have tried Ebay selling a couple of times and flopped. I am also new to dropshipping and setting up a business..

I have found a supplier in China and want to sell their products online as well as on Ebay.

So how does the pricing work.. If I import and resell it is straightforward.. I import, pay duty and taxes and then mark up and sell

In drop shipping how would this work.. I take the supplier price.. add postage charges and advertise this price.

Now when I have ordered stuff on Ebay, sometimes I have been asked to pay tax to the courier company on behalf of HMRC.. but sometimes I have just received it without any call for taxes. How do I add taxes to the price I charge customers where customer receives goods directly from seller.. what if my buyer receives a notice to pay taxes.. If I have quoted an all inclusive price, can I pay this tax to the courier company on behalf of the buyer.. How does this aspect work.. Can someone please throw light on this

Thanks