Yes you do! While the supplying of such spectacles by supermarkets and chemist shops, and even my local library, means that the public can buy ready readers just about anywhere, it is not reasonable for a member of the public to expect a professional service from the local supermarket. You, on the other hand, a registered professional, can reasonably be expected to give such a service. You should, when supplying ready readers, fit the frames as well as is possible with the quality of frames; guide the purchaser to the correct power for the usage of the spectacles and advise that regular eye examinations are necessary to protect their ocular health. This advice, together with details of the product sold, the name, address and date of birth of the purchaser, should all be recorded.
It does seem hard but the choice to supply such items is yours. If you are unwilling to give such a service at the recommended retail price, perhaps you shouldn’t stock them at all. It may be wise to let patients experience the difference between unqualified sales and those of a professional, registered optician.