I would never buy good apartment rating reviews with gifts.
I will treat everyone who walks in my door, including all residents, former residents, prospects, or vendors, with the same level of kindness.
I have found that asking everyone for reviews- including any unhappy former residents, I get better reviews. Even the residents who left my community because they were unhappy usually have something positive to say if we are sincere and kind.
Even though it's an uncomfortable conversation, I think it really helps to communicate move out costs rather than surprise former residents with them after the fact. If you meet with them and honestly tell them what they will be charged for, their anger about the charges has time to difuse before they move out, get the bill, and get motivated to post a negative review.
I know, your question was "without going into ethics" but this is something I'm very passionate about.