Does matt paint mark easily is a question that needs to be asked a little more often.
First though we need to know what type of matt paints there are available.
Usually if you walk into a paint shop and ask for a bucket of paint for your walls the shop assistant will ask if you would like an acrylic matt paint or maybe a more durable washable matt. The acrylic matt is a good solid paint that can be wiped clean to a small degree. This acrylic matt has a very slight sheen and will suit most situations. The washable matt is a more durable paint though it can take more coats to cover. A washable matt can usually take a good scrubbing and is perfect for hallways and high traffic areas.
Another option is a chalky matt. A chalky matt doesn't have any sheen at all and is perfect for ceilings but completely rubbish on walls. You don't want chalky matt for your walls
There are lots of excellent paint brands available and lots of types of matt paint ranging from good to excellent. With the good paint brands you can expect decent durability from their matt paints, whether its a standard acrylic matt or a washable matt, all should be well.
If you are having a colour mixed into a matt paint then you need to make sure its mixed into the correct 'base'. The paint base is a foundation for the colour. Occasionally some painters will have a colour mixed into a bucket of white paint as it can save money. This is bad news for your paint and colour. It will deliver less than par results.
What's all this have to do with the question, does matt paint mark easily? I'm getting to that. Most colours are light colours and mixed into light vinyl matt bases, these are usually pretty solid and hard wearing. Problems arise when darker colours are mixed. No matter the paint brand or type of matt paint, if its mixed to a dark colour there's a good chance it will mark easily.
We carried out a job recently for a couple in Phibsborough. For the living room they picked a dark colour mixed into an acrylic matt paint. The walls were prepared as usual and 3 coats of this dark matt colour was applied and it looked great. The problem was this dark acrylic matt paint marked very easily, so easily that if you touched it anywhere a chalky mark would be left behind. The paint company were called in and explained to us that with these dark colours.
This is what we were told - When you make a dark dark colour - the level of tint and dye needed to make it is so deep you need remove some of the resin, because it physically has to fit in the tin, more dye than resin. So its not as durable and tough. When you brush up against it, the surface of the paint becomes flattened and that creates that matted or burnishing smudgey effect. There's nothing much to work around it - you can get a very damp cloth and give the smudges a bit of a wipe - just the once or twice as a fix. For really deep products we don't make them washable matt.
If you look at the small print, most paint manufactures will say that darker colours may smudge. Regardless of wether the colour is mixed into an acrylic matt or washable matt. The solution? Don't use matt paint for darker colours. If you want to use a dark colour then consider getting it mixed into either a soft sheen or acrylic eggshell. This way there's a good chance it won't mark so easily!