There are hundreds of eikaiwa. These schools teach the students at locations all over Japan. The best locations are considered right in front of important train stations or on the route students or workers take to or from a station. As for the work, you can find yourself teaching at the school's location or being sent to the client's site. Schools differentiate themselves in the marketplace by factors such as price, teaching materials, location, class size and type of teaching.
Looks are certainly a factor in the eikaiwa business.
There seems to be a bias towards blonds, and an emphasis on hiring young, attractive teachers. Some teachers will dye or tint their hair blond. Turnover is very high at many of these schools and the schools are not necessarily unhappy about this because new teachers are fresh and enthusiastic and try harder. After they begin to burn out they can be easily replaced. Two complaints frequently heard by ESL teachers new to Japan concern teaching hours and travelling.