Only had time to watch the last one so far.
Against Marshal blitzers the worst thing to do is exchange Marshals . Your exchanging Marshals is part of the blitzer's plan. Better to retreat the Marshal when you had the chance as he would not have followed you for fear of the Spy.
In that game though your set up was vulnerable to the blitz as you had flag bombed near left corner .Whatever you do or don't do you will soon have problems in that scenario. If he had been a player who blitzes his opponent's right side then you would have had an easy win.
If you think you are going to play a blitzer - at ELO 350-450 it is the most common strategy - then i always think a central flag position is best , with the Spy positioned centrally also . Marshal Blitzers almost always attack on one side or the other (usually the side this guy did it seems to me) .
With a central flag when the blitzer comes down the left or right don't move anything on the side being attacked . This will ensure he loses most of his Scouts cheaply . He will also - if you leave everything unmoved - likely bring in a couple of Miners that will be wasted as well . That's another fun thing with the blitzers ; they have 2 or 3 Miners that follow the Marshal and scout ahead of him, their other 2 or 3 Miners will be stuck miles away on the back row of their weak side and you can usually find and kill those with a Captain mid game .
Personally , while he was blitzing with the Marsh i would keep my General hidden , as his Gen likely will be hidden behind lake ready to exchange with yours as he expects you will rush it straight out and hopes you just get a Scout or Sergeant before exchange .