In looking at thier feedback they have sold these types of eggs and many more with 100% positive feedback. I would guess they are really that dark. I hope someone who knows the breed will come along and answer your question.
I did not think they look "bright" red, but it could be my really really old (like 8+ yrs) moniter. It could also be their camera did not get the color correct???? When I buy off ebay I look at their feedback and theirs does have lots and lots of eggs they have sold, including ones listed just like these. You could also send them a message asking for another pic, or if the pic they posted is off on the color.
Don't know if the camera or your monitor made the color look redder, But I did notice they have a really high feedback and 100% feedback rating- So they must have good eggs. Don't marans eggs sometimes lighten and darken up at certain times. maybe email the seller and ask if they get darker at certain time or not. They evidently are pretty honest or somebody would have complained.