Tom McPhail, head of pensions research at Hargreaves Lansdown, has expressed concerns about the guidance service, which was further detailed by the Treasury yesterday and said there is "huge job" for the FCA to regulate it.
He said: "The Treasury is opening the door for further product design: more flexible annuities which allow longer guarantees and one-off payments; and other complex products with intricate guarantees.
"It will become increasingly difficult for ordinary investors to discern whether they are actually getting a good product or not. In many cases it will be unsophisticated investors with relatively small pots of perhaps only a few thousand or tens of thousands of pounds.
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"The guidance guarantee will not help them here as it will not provide specific product advice, and paying for an independent financial adviser may be too expensive to justify.
"There will therefore be a huge job for the FCA to do in policing these new products, and the sales processes around them, to ensure that investors are sold competitively priced and appropriate products.
"Without this regulatory scrutiny, these pension freedoms could be nothing more than a misselling charter."
The FCA's role in the guidance service was made clearer yesterday.
It outlined a raft or proposed rules and standards for the 'delivery partners' involved.
Among the key points it laid out were that the delivery partner must not recommend specific products, providers or financial advisers to the consumer or sell any products directly or indirectly to the consumer.
It said the delivery partner must ensure that all those who approve the design of any processes and tools, including web-based material deliver the guidance over the phone or in person are competent and have sufficient knowledge and expertise to do so.
The FCA launched a consultation on the standards, which ends on September 22.
Mr McPhail added the Treasury had been 'sensible' in opting for independent bodies like MAS and TPAS rather than pension providers to deliver the guidance, though he questioned if they have enough resources to manage.
The Treasury said guidance will be offered through a broad range of channels, including the internet, by phone, face-to-face.
It will be free to the consumer, funded by a levy on regulated financial services firms.