The legitimacy of the data that is being resold is a key factor in data theft in illicit markets. To ensure that customers can make purchases with confidence, a variety of services are available to validate information such credit card numbers.
Criminals are also acutely aware that anyone, but especially security researchers, can want to obstruct their activities. Although it can occasionally be ineffective, spamming phishing pages with useless information is a sport unto itself. Defenders can follow the money by using specific cards for tracing purposes.