If the project has all the legal approval in the place then i am sure that the builder will provide you possession on time. So, ask for the legal papers, verify it by a legal expert of ur locality and then proceed. Now-a-days, possession delay has become a fashion for the builders all across the city. As per report, 25% of yearly launched project getting delayed only because of lack of approval.
If you want to check the credential of any builder then just search in google with the company name. You will get lot's of reviews on several property portal. If the builder is good then no negative information will be available and if the builder's track record will be poor then lot's of discussion will be going on. Or you can check in their website that how many project this builders has successfully delivered. And how many still under construction.