I've been developing for someone, I'm new so it's all free thus it's for experience only. I say that because you'll likely notice lots of errors here that I'm not aware off and boil your blood because someone could be profiting off such tripe!

anyway:

They're the bulk of my tables, it's all important.

http://i.imgur.com/8wbL4.jpg

I'm having trouble deciding the relationships. Here's what I think you should know:

A customer can only be an exhibitor, trader, food vendor or weekender.
A customer cannot be more than one of the above.
The aforementioned can only be one registered customer even if they bring x amount of staff.

That tells me it's a simple 1-1 relationship. At first I thought they were 1-n but I'm convinced they should be 1-1. If I create a form I get a lot of errors, although 1-n worked fine when I had that set up (you'll notice multiple IDs).

The reason I've kept customer types separate and not just included a field determining the customer type is because different data is stored depending on the customer type.

So, am I handling this the right way? or do I have my wires crossed?

thanks.

do a search for supertype/subtype -- i believe you are on the right track

well, except for the additional id columns (foodvendorid, etc.) that you are assigning to customers

I see it alright, although those address lines seem kind of suspicious. You may have to normalize some tables a little, so I recommend you to read about normalization as well as what r937 told you.