While you can't create limitations against their lease and legal rights they have for quiet enjoyment, things like keeping common areas free of clutter or routine maintenance items that are tenant responsibility can often be added to help keep the expectations on both parties clear.

I'm not right at the beginning but still new enough that I'm not getting too cluttered up or anything.

It's been a lifesaver for removing things like reflections in mirrors or clutter that was missed during a showing.

I wouldn't put too much stock into their opinion because if they're not going through that problem... the website won't speak to them at their gut level... and they'll just look at all of the words as "clutter" that doesn't add value to them. 

All trash and clutter removed. 2.

Don't get distracted by clutter, odor, obsolete fixtures or appliances, wall or floor colors, etc.

I also think that its organization should be very simple without too much stuff cluttering it.

This can backfire on you though if the property is not in good shape- I mean cluttered.

.- Cabinets look good but I'd get rid of all the clutter above.- Take all the cheap prints off the walls. 

I suppose it could also just be some random disgruntled citizen that knows they're against city code and they don't like them cluttering up the side of the road.