Cost is, of course, where FreeMerchant scores highly, because the service is completely free - there are no set up costs and no ongoing costs. However, as you would probably suspect, free really means advertising supported. Each FreeMerchant store currently carries three small ads at the foot of each page although there is nothing in the Terms of Service to prevent FreeMerchant increasing the size or frequency of these at a later date. On the subject of the Terms of Service, I found many of these to be particularly onerous or restrictive. For example merchants are not allowed to include any advertising or external links on their pages.
Most people just skip over the agreements when signing up for a new service.
If you do decide to go with FreeMerchant make sure you carefully read and understand the Terms of Service. Order processing One simple form is used for setting up the major order processing options. Unfortunately, there is no ability to define rates for international shipments. FreeMerchant also has a very poor method for dealing with Sales Tax. There is no capability for sales tax to be automatically calculated - the merchant has to manually add an amount to the final customer invoice when processing an order.