Hi
@Laura thanks for your question - you won't be the only one wondering how to go about this.
BRC's agents and broker standard is pretty flexible on this because they are quite practical. They know that when you need to buy and sell products, you need to be able to function as a business. BRCGS is giving us deliberate flexibility on this point.
A contract is simply an agreement that's enforceable, right? Even if that's an online purchase then it's all the details supporting that online purchase. Just as an example I say I talk about online purchase because this is the way the world works now. Although there is no definition in the glossary for contract, the clause is giving us the other option of specification, as you rightly pointed to. The glossary says this about a specification: An explicit or detailed description of a material, product or service. Again whether you purchase via an email quote, which gives you all the necessary information you need about the material, or whether you make an online purchase and the product listing gives you all the information you need to ensure that you get the product you thought you were going to get, then that clause is covered.
To answer your question more specifically, what a contract or specification must include is enough information for you to be satisfied that you're going to get what you need. If you don't, you can go back to the supplier and complain. I bet you can imagine how very different this would be for a paper clip versus a mobile phone and that's why BRCGS can't be specific. They're happy to give you flexibility so you can apply your expertise here. Your example of the UV-protection clothing is perfectly demonstrating your expertise. Apply that in a simple document showing what you believe to be low vs high risk items or properties of those items and the auditor is going to be happy. They know that sites are the experts and it's only where they see a risk that the site hasn't addressed that a non-conformity is then a possibility.
Last point to make here, clause 3.7.4 in the A&B standard even allows for a historical trading relationship (again, only for something you have assessed as low risk). I like this, very practical. If you've been buying those Tshirts from your supplier for a few years and everyone is happy with the product and the service, why change anything. Just pop that in your risk assessment and
Voilà.