Both Samsung Electronics and LG Electronics have started to buy back used smartphones and implement other promotion programs in South Korea, as they try to boost the sluggish sales of their latest flagship devices.

Despite the much hype surrounding the Galaxy Note 9 and the V40 ThinQ, Samsung and LG largely failed to ignite interest in their latest premium smartphones.

Samsung on Tuesday began a trade-in promotion allowing Korean consumers to trade in their smartphones and receive cash rewards when purchasing the Galaxy Note 9 smartphone. The company also doubled the trade-in values of specific smartphones such as the Galaxy S7, S8, Note Fan Edition and even Apple's iPhone 6 and 7 smartphones.

Used smarthones eligible for the trade-in program should not be damaged.

Samsung claims that it sold 1 million Galaxy Note 9 devices within 53 days. This is about a week late compared to its predecessor Note 8. The firm had sold 11 million Note 8 smartphones last year.

LG Electronics also unveiled its preorder deals for the V40 ThinQ smartphone Sunday, and customers who preordered the smartphone can replace their smartphone screen and back cover for free within a year of purchase.

The V40 ThinQ will go on sale here starting Oct. 24 and LG is currently taking preorders. The price tag of the phone is 1.05 million won ($931).

LG said it also offers an upgrade program for people who purchase the new V40 ThinQ. They can receive cash rewards up to 40 percent of the purchase price of the smartphone if they repurchase LG's latest smartphone.

Those who buy the smartphone by the end of next month can also join the prize lottery for LG's popular home appliances.