A retail agent otherwise known as a travel agent was for many years the only public face of the travel industry. They sold packages from brochures. Some travel agents were tied or owned by a tour operator. Others were independent, sourcing packages from tour operators and tour organisers.
In many ways, travel agents are very similar to tour organisers. For me, the difference is that a travel agent builds the business around their retail space, traditionally selling standard packages.
This is a different emphasis from a tour organiser who is less likely to base the business around retail space and is more likely to tailor packages to suit individual groups of customers. However, that said, a tour organiser could be based around a shop, and a travel agent could concentrate on tailoring packages.
Becoming a travel agent requires access to package providers, the ability to run marketing campaigns and a retail outlet. While the set up costs may well be higher than a tour organiser, due to the cost of the retail space, it is a viable start-up option.