Thanks! The OP is pointing out how a common pitfall can be encountered by DDFers or anyone motivated to meet a spending threshold or getting extra points.
The same caution should be heeded when signing arvus on a chov. (guarantor on loan, ponyatno?) or stam lending someone cash or credit. The general principle is do not take on a risk that you can not afford, for example if you cosign a loan for $500, first think if you will be stuck with the debt if you can handle it.
There are mekoros for avoiding cosigning in general, as mention that not just the money but also the relationship can be ruined.