Yes, dont under estimate debt collector, there are lots of legal ways to get pple to pay up, eg send legal letter of demands, followed by filing a court writ of summons, and then writ of seizure on the assets in the house, and lastly bankruptcy if the amt is more than 10K SGD (including interest fees, admin charges, legal fees etc).
i know of a case where a debtor owed a bank 1000+ sgd after paying majority of his debts, he refused to pay the remaining 1000+, the bank managed to get a court order to seize his assets in his landed property. and this guy had to pay up in the end, while incurring more legal fees.
So don't play play with debt collectors