I have read in a couple of places on how RBI has come down severely on PayPal accounts, blocking them etc... Is it a big issue and is there a risk in opening PayPal accounts for a B2B marketplace going forward.
What are the restrictions put on Paypal vs. other payment gateways?
Its not the first time Paypal services are restricted in the name of regulations. As you said B2B market place, I wont suggest Paypal.
It may be useful to know what kind of B2B you're involved in. If its international trade look at LC or Down payment methods.
Other Payment gateways aren't imposed any such regulations like maximum amount per transaction and Limiting number of Verified transaction per account.
All i could say is Western Union and similar payment gateways are good. but they dont have such transparent system as Paypal does. Paypal's regulations mostly affects bloggers and software developers in India since their customers are overseas and the projects doesnt need any meetings in person. If you are in trading and B2B the safe way to transactions are through govt approved banks.
For other payment gateways check here