Massey University Chinese marketing specialist Henry Chung said the promotion was an "innovative and bold move" by the agency, where seven out of 10 of its clients are Asian, mainly Chinese.
"Mercedes is traditionally seen as the most luxurious car brand among the Chinese, and this brand is associated with prestige," Chung said.
"The returns on selling property is so high, the agency will have no problems in recovering the cost of the Mercedes that's being offered as a sales promotion tool."
Chung said apartments are often not the property of choice for most Chinese and extra incentives were needed to motivate them to buy.
"The majority of Chinese buyers prefer to buy stand-alone houses with land if they can," Chung said.
"A lot of people are coming to New Zealand because they would like to change their living environment, and that's not apartment-style."
James Law said the promotion was being offered in collaboration with Mercedes Benz North Shore.
He denied the promotion was aimed at enticing the Chinese.
"It's about bringing together two products that are associated with luxury and prestige together," he said.
"This is also how we can differentiate ourselves from the competition."
The agency will start advertising the free car with apartment purchase offer within the next week.
Chelsea Bay Residences is a freehold development designed by Auckland architects, Leuschke Group.
All units consist of two bedrooms, a private balcony and range in size from 88sq m.
Construction commenced in June and is expected to be completed by early 2018.
Law acknowledged that immigration rule changes will hurt the residential apartment market.
"Many apartment buyers are parents of international students with hopes of moving to New Zealand through sponsorship of their children," he said.
"The changes in immigration rules will now give them no more reason to buy."
Immigration changes made last week included temporarily closing the parent category to new applications and reducing the number of places for family members of migrants from 5500 a year to 2000 a year.