I don't see why so many people use wordpress and Joomla for sites they are not intended to be used for. Joomla is a CMS and should be used for websites that distribute information, not a whole auction website. I would highly suggest you create your own website using PHP and get it rigorously security tested.
Thats kinda like saying bit coin shouldn't be used for paper money when all over ebay and amazon people are selling paper wallets. Not to mention that wasn't the question I asked.
Fyi Joomla has high end PHP security "extensions" so writing my own would be up to me.
That as maybe but if your asking if its a good idea, by default it prob isn't as you would not need to ask.
I suggest you find something that isnt everywhere and develop that !