Since we can't fortell the future I guess the best advice is to listen to your heart. If you're of the mindset that you want a child regardless of where he/she comes from, you may want to work with an agency that deals with multiple countries so in case something did happen with China, you may be able to move your focus to a different country. I don't know all the ins and outs of how to do that but I'm sure someone else here does
If you're like me and you're deadset on China, you may want to deal with the agency of your choice, even if they are China only.