It is a service, but not one that is needed. There are sites that do this and they allow for escrow, so there is at least some protection. Those sites act as a connection service between those selling and those buying bitcoins and because of that fact, they are outside the KYC and other regs that fall all over your site.
That means that you need an MSB and need to comply with the KYC and other standards, because you are conducting direct FIAT to crypto and that has been made a pretty clear cut set of regulations.