How important is knowledge of fengshui for someone involved in real estate in China?

Personal knowledge doesn't matter but I would suggest you have someone who knows fengshui assist in all designs. There are a fair number of people including wealthy and powerful people who believe in fengshui and if your property doesn't meet the proper layouts they will walk out and refuse business with you. Even non fengshui believers will find a hard time because someone they know will be and advise them against it. If the energies don't align in a proper way by fengshui belief your business will struggle simply because those who believe will avoid you.