The 1st-generation idol has a history of being sued for fraud. He was sued in September 2013 after borrowing 1 billion KRW (approximately 930,000 USD) from 3 people from 2009-2010 and not paying it back. He was found guilty and was sentenced to probation. He was sued once again in 2015, but had been found innocent in that case. 

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He has now been sued by 'K'. In November 2010, he borrowed a total of 142.2 million KRW (approximately 130,000 USD) from 'K', citing that he needed to pay up for a Japanese concert that had been cancelled. 'K' let Kang Sung Hoon borrow the money and sent the money to Kang Sung Hoon as well as to 'N', who lived with Kang Sung Hoon at the time.

However, afterward, Kang Sung Hoon started avoiding 'K's calls and did not pay him back either. When he finally got to meet Kang Sung Hoon, Kang Sung Hoon told him, "You gave the money to 'N', so ask him for the money back. Why should I pay you back when you didn't put the money in my account?"

'K' ultimately decided to sue Kang Sung Hoon after seeing him promote back with Sechskies despite ignoring all of his calls. 

YG Entertainment has not made any statements.