Legally they cannot negatively affect your credit rating. They may choose not to finance the next car, but there are plenty of firms that will
You effectively mutually agree to cut the hp term short in accordance with the terms of the agreement. Which is nice.
Hence, when my Seat went back at month 25, it was in near mint condition even allowing for 130k on it and they didn't even blink even though it had dumped £10k in value from the £12.5k purchase price (a pre-registration reduction from £16.5k) down to £2.5k.
It affected my credit so badly (not) that I was subsequently able to finance a further 6 cars to the tune of over £62k over the next 6 years. And all alongside two personal loans of £25k, a couple of credit cards and a marine mortgage.
Consumer credit is as freely available as the napkins in McDonald's.
None of which is a reason to finance a car. Also, you only need a credit rating if you intend to borrow money, mortgages notwithstanding as these can be manually underwritten. The point being that not having a credit score, as opposed to a low score, shouldn't prevent you from buying property.