Private agencies offer attractive interest rates. Donot rely on private firms. When compared to the rate offered by them with Nationalised Banks, you will find that the interest offered by private firms are high. But their interest calculation is different from the Nationalised Bank's calculation. At a glance you will be confused. Nationalised banks calculate compound interest compounded quarterly.
The best thing to do is check the firms past records. See if you can interview any clients that you pick, not them. Find their SEC filings for the past year and see what they have been up too. And if it sounds too good to be true, it usually is.