Business Rules :-
A Part must have at least one Supplier

Questions
what is a Brand ?
What is the difference between a Source and a Supplier ?
Here are the Specifications for the customers and car Parts Database :-
An automotive aftermarket parts distribution company based in the UK is looking for Multi user cloud based/web solution.
Linking multi car parts (database) - Multi brand/supplier - Multi purchasing sources/buying price -Multi sales pricing. 
Most of this can be done in excel but, this time consuming and not central based. 
Appearance , easy of use and functionality to run multitude of reports within minutes. 
End definition to hold multiple fields on each part,link as many suppliers (holding multiple fields) to each part and 
hold sales information on each part(pricing) etc. 
if you are able assist please do contact us.
Regards
TJ