I've ask open ended questions that gravitate towards this. what do you want changed (what they get out of it is a possibility to change annoying or lacking items) What do you want kept the same (what they do like about it) what would you tell your friend (that way its honest)
I think there should be interaction with client everyday so that you get feedback everyday. That is why client and developer coordinators are essential for any project.
Here is something I have done and has worked well. Go to fiverr.com and there you can find individuals who for $5, will put a positive comment/review on your site. May not be the real stuff, but to get started, it works. Good luck.
once you sold your product or service and if you think client is happy. ask him for a review in exchange for a bonus or link. he should be happy...
If your product or service has provided great value to the customer, getting a review is easy and just needs to be suggested.