Monograms -- Many collectors view old, elaborate monograms as a lost art form and historically important. It does not detract from the desirability or value of a piece when a monogram is present. Most pieces are, however, even more valuable without a monogram. As you become more familiar with silver, you will be able to detect monogram removal. Monogram removal can damage a piece of silver and significantly reduce its value.
Authenticity -- Some collectors frown upon pieces that have been updated, such as those with replacement knife blades. Silverplated blades are often found with wear. They can easily be replaced on hollow handle knives, so some collectors prefer to have them refitted with stainless steel blades. However, stainless steel was not introduced in flatware until the early 1920s. This is one of those aspects of collecting that can be a matter of personal preference, but you do need to be aware that your flatware may go down in value if you alter the knife blades.
Repair -- Dents, disposal or other damage can be repaired by a silversmith. Pieces can also be replated. The cost is prohibitive for more common items, but is certainly worthwhile to restore rare antique pieces.
Modified Items -- Be aware that these exist and learn how to determine if a piece has been modified from its original state. Common flatware pieces are sometimes altered to make them appear to be more rare and valuable pieces. For example, spoons are sometimes cut to resemble ice cream forks or a sugar spoon may have been pierced to resemble a sugar sifter. Look for signs that pieces have been modified and avoid purchasing them for your collection.
Forgeries -- New forgeries in popular and rare patterns appear for sale regularly on the Internet. In particular, salt spoons and rare pieces such as asparagus servers. Many of these pieces have no maker's marks. Further, forged maker's marks in silver have appeared for hundreds of years. The age of a piece does not necessarily indicate it's authenticity so learn as much as you can before investing in an expensive piece.
Educate Yourself -- Many good silver books are available in the collecting section of your local book store or library. Sullivan recommends these titles on marks: