In MY experience, the adjective "mala paga" has ALWAYS been applied to specific persons (Fulano es mala-paga)...NEVER to all or most Dominicans....And again, the specific socio-economic group or "class" they were referring to is critical...They may have been mostly thinking or referring to people in THAT class, as opposed to 10M Dominicans.
To my knowledge credit-reporting agencies, collection agencies, "repo" men, credit-repairing schemes, credit cards for bad-credit people, etc. etc. are ALL alive and well in many countries other than the DR, including the US and most/all "developed" countries... and no, I do not believe such things were invented specifically for the Dominican community (if any) in those countries...That tells me that the phenomenon of people who do not or cannot pay their bills as regularly as needed ("mala paga") extends well beyond the DR, and developing countries, and is by no means exclusive to Dominican people.