9.3 is understandably similar, although not identical, to section 4.4 of the Agents & Brokers standard.
We have Traded Goods excluded from our BRC Food scope as we maintain separate certification under Agents & Brokers, but the broad intent seems to be the same - there are slight difference perhaps due to the expectation that most Agents won't have access to their own testing facilities.
Nonetheless I'd take the same approach for both, and make use of the provisions of clause 9.3.2.
You can rely on the analysis provided by your suppliers, subject to you being able to justify this position - presumably you'll have e.g. supplier assessment records with detail showing that the analytical methods they use are appropriate, the people doing the testing are competent, everything is calibrated etc. Combined with your tracking of complaints/issues this should suffice, but the expectation is that you'd be addressing this more proactively than simply waiting for your customers to tell you if there is an issue - broadly, you should know, or at least have reasonably significant confidence, that the product is right before you supply it onwards.
Do you use any of these traded items in your own production?
If so, you can perhaps come up with a position whereby you don't routinely sample every batch, but the bulk of your monitoring to ensure that suppliers' analysis is correct / products are in spec can be from your own QC testing prior to using the products.
The standard does state "independent product analysis" under 9.3.2, so this may come down to auditor interpretation - for Agents & Brokers we've found that the expectation is that the analysis is independent of the manufacturer, but equally this could be viewed the other way and be an expectation of genuinely third-party testing. The Interpretation Guide doesn't actually clarify this point though.
Otherwise you may need to come up with some sort of schedule to sample a proportion of the traded goods, and obviously as it's BRC you'll need to determine this by risk assessment...