Might be income ceiling issue, maybe lower wage, but some people is lower wage but got many sources of income not shown on CPF statement.
In-house or external, they are all a business run by people, there are rules and regulations. To go under DRS, might have already occurred a lot of bad debts and the interest is spiraling out of control, so one takes it up. This is still bad credit rating.
Bad credit rating refers to late repayment, high loans/credit card outstanding amounts with difficulty repaying etc. If you are a bank, finance co, would you dare to loan? We are not talking 1K or 2K, we're talking about 60-70K for a Mitsubishi Attrage (assuming 40%/30% down).
The reason to have a guarantor is so that if the buyer MIA or cannot pay, or the car is missing, where they can't repo, they can go after the guarantor.
I don't think TS is the former, so, sad to say...