Start with the same base
Use the same model, variant, registration timing, financing assumptions, and trade-in treatment. Otherwise, the two packages are not directly comparable.
Separate price from extras
Write down the cash rebate and each included item separately. Ask whether accessories are original equipment, dealer-supplied, or third-party, and whether installation affects warranty coverage.
Value benefits conservatively
An accessory's advertised retail price is not necessarily what it is worth to you. If you would not buy it separately, do not treat the full stated value as a saving.
Record expiry and conditions
Monthly promotions can depend on registration date, available stock, colour, bank, or insurance package. Keep those conditions next to the headline value.
