So, your commercial painting contractor is recommending a flat finish but you’re curious as to how well it will stand up to wear and tear….
Perhaps your commercial painting contractor is recommending eggshell. Although you prefer the flat finish, you might be concerned about stains and 
smudges on the walls… Or , Maybe you are a commercial painting contractor and you want a quick and accurate answer to your client’s question, “Flat or Eggshell, which is better for wear?”
Regardless of who you are or why you want to know, you’ve found the right article to give you the answer.
First a Bit of Paint Tech 101
House paint is made of essentially 3 main ingredients plus additives. All house paint contains a carrier, pigments and resins. With regard to wear and tear, the key to durability is the amount of resin.
Resins, the plastic-like ingredients, account for two primary characteristics of house paint: finish and binding effect. Higher resin content = glossier finish. Flat paint has the least amount of resin while glossy paint has the highest concentration. As far as binding effect, how well the paint sticks to the wall, the more resin the better it adheres.
Resins also account for how porous or absorbent the paint is. Paint with higher concentrations of resin are less porous so the paint is not as easily absorbed by the wall surface as are paints with lower resin levels.
The Logical Conclusion
Since eggshell contains more resin than flat paint, eggshell is easier to wash and will wear better and longer than flat paint. 
However…
Paint quality has a significant impact on paint durability. Higher quality paints contain more solids (pigments and resins) so when the carrier evaporates there are more resins left on the wall which makes it more durable. Also, look for paints that are 100% acrylic latex not vinyl acrylic for longer wear. A high quality flat will wash better than a low quality eggshell.
One Other Option
If flat paint is desired there are several flat enamel paints that contain special additives specifically for wash ability and durability. These paints are general more expensive but in high-traffic areas where a flat finish is desired 100% acrylic flat enamel paints are perfect.