If you are really serious about the project then you can always hire testers. It will cost you a chunk of change, but it can be really worth investing in experienced testers who can look past what the game is currently and help you point out problem spots early on. This is especially true if you happen to be doing mobile app development. (Sculpin QA for example has multiple copies of every model of apple mobile device in house with most versions of iOS installed. Plus most of the popular android devices.)
Even if you are only able to contract a few hours at a time it can be worth it. You don't have to go chasing after a testing house to give you feed back, and a bad release put in the hands of a testing house isn't likely to have a negative impact on public opinion if you've screwed something up as they're bound by NDAs.