So, let me get this right...
We're in a 'club' (the EU) and we don't all get along, but put up with each other because we think there's a common benefit...
Then one of the lads says 'I don't want to be a member any more, I think you're all a bunch of wasters'
Then two weeks later, that lad is supposed to negotiate individually with each of those nations to cut itself a better deal?
Yes, we have goods they want, and they have goods we want... but we import more than we export and there's more of them. I'm really not convinced we'd be holding the upper hand!
Ah, some will say - but we can now negotiate with America or China and cut our own lucrative deals.
Hmmmm - those are two extremely large markets / economic powers, we've just left the EU and are in an 'unstable' condition and we're going to renegotiate a BETTER deal? - dream on.
Every other nation on earth will know that after an EU exit, we'll be 'needing' some results - that doesn't strengthen us, it weakens us. Furthermore, who is going to cut us a better deal and risk losing the far larger market - the EU? It's like undercutting the deal you have with your major customer to please a smaller customer? - business suicide.
Of course, there will be SOME wins - businesses that couldn't sell successfully to the EU could now sell to us, but they aren't going to be improve the quality and safety of their products, they're going to pleased they don't have to meet EU regulations.
You make it sound as if we've got to start wheeling and dealing on June 25 if Brexit win. There are two years before anything will change at all and two years is a long time to organise ourselves for the deals that will follow. It won't be governments doing the horse trading either. It will be businesses. If you think Merkel and Co are going to tell Volkswagen and Bosch etc what they can and cannot do trade wise then you have been taken in. Tariffs will be decided by those directly involved and Merkel and Co are going to have to listen and act on mutual interests.