Please guide them to these links for commodity code guidance:
Trade Tariff: look up commodity codes, duty and VAT rates – https://www.gov.uk/trade-tariff
UK Global Online Tariff: look up commodity codes, duty and VAT rates – https://www.trade-tariff.service.gov.uk/sections
Economic Operators Registration and Identification number (EORI).
You need an EORI number to move goods between the UK and non-EU countries.
Since 1 January 2021 you have needed one to move goods between Great Britain (England, Scotland and Wales) or the Isle of Man, and the EU.
You may also need a separate EORI number if you move goods to or from Northern Ireland.
If you do not have an EORI, you may have increased costs and delays. For example, if HM Revenue and Customs (HMRC) cannot clear your goods you may have to pay storage fees.
Standard industrial classification of economic activities (SIC) codes relate to the business activities, rather than the load being carried.
If just a haulage company carrying cars and parts then the SIC code could be “49410 – Freight transport by road”
If they are the exporter of the car or car parts then there will be different codes for these. See below
The below GOV.UK website has 2 PDFs to download – 1 for Custom agents and 1 for Fast parcel Operators.