Here's a quote from an interesting article on eBay about buying ephemera at estate sales :
Avoid dirty paper, no matter how cheap it is, you can't wash paper and once you have spent your money, all you have is dirty paper. Water is the kiss of death to any form of paper, except Victorian trade cards. Those can be put in warm water and soaked to get them off paper, but that is another article altogether ! Sometimes we have been given boxes of paper if we will just take them away from the sale and for the first few times we thought - hey, hey, what a deal. Then we learned we had a box of dirty paper and all we were doing if filling up our trash cans with free boxes of dirty paper. Paper that has little bugs will be paper with little bugs at your house. Basically, if you hold it and touch it and you get dirty, or it crumbles, all you have there is dirty paper.
Look for paper that still has a clean line, clean look and most of all is clean. Many estate sales will take the time to put paper in plastic bags, to keep them clean during the sale. This means care has been given but it doesn't necessarily mean a high price on the item. We have seen people pay way too much for paper items because they were in those nice plastic bags. You want the items to be clean but it doesn't mean they have to be inside a protective seal. We have found some wonderful paper, stacked neatly in a box and nothing was covered. Often mid-century teacher's supplies are some of the greatest finds because that era had bright colors, die-cut lines and a good cardstock as the printable service.
This is all so very true. There are some nice tips online about how to reduce the mildew on paper items but remember -- some mold is toxic. If it's just odor and no discoloration or visible mold/mildew, you'll probably be okay to treat it. For me, I'm afraid that quite often mildewed paper gets scanned and then *gasp* tossed out. I live in a 100 year old house and we don't need any added allergens around here what with 3 dogs, 1 cat, 2 grandsons and a garden.