There is nothing wrong with buying banks that have repairs and restorations or are later castings from original castings or are reproductions. Great looking banks that have well done repairs can be added to a collection for less money than a mint condition bank. But it is not a good thing if a collector buys a bank and doesn't know what it is that he or she is buying.
If you're think you're buying champagne, you don't want it to turn out to be sparkling cider!
1. Whenever there is an opportunity to look at a quantity of banks, whether at an auction or in a collection, go and look at them in detail. Take the time, even if you know you aren't going to be buying anything right then. Just go and look and look and touch and feel. Challenge yourself to find repairs and to figure out if it is an old original bank or a later casting.
2. Buy reference books on mechanical banks and read them. The best ones are The Bank Book: The Encyclopedia of Mechanical Bank Collecting, 1985, by Bill Norman, Penny Lane: A History of Antique Mechanical Toy Banks, 1987, by Al Davidson and Official Price Guide to Mechanical Banks, 2007, by Dan Morphy. There is also a book of the base tracings of original banks by Robert McCumber. This book may be hard to find but is useful for determining whether a casting is original or a second casting (which may be smaller). (But there can be some exceptions to the general rule.)
3. Learn how to use a black light and carry it with you. Be aware that not everything that shows up under a black light means that there is a restoration. It is a tool for examination (but it is not infallible). Learn how to interpret the results of using a black light.
4. Carry a magnet with you. This is useful for determining whether a bank is made of iron or not and whether there are repairs made of other materials.
5. Look at banks that are confirmed to be reproductions or fakes so that you can see how they differ from old original banks. Examine their surfaces, the paint, and the quality of the casting. Look at how they fit (or don't fit) where the pieces meet.
6. When examining old banks, look for areas in the paint that look uneven and bubbled. A welded break in iron burns off some of the original paint in the area of the weld and is usually touched up with new paint.
7. Compare the paint on different parts of a bank to other parts of the same bank. Does one color look the same on all areas of the bank? If it differs in gloss, texture or hue, ask yourself why it differs.
8. Check to see how tightly the pieces fit together. Old banks generally were made to fit together very well.
9. Look at the small component parts of the bank. The figures, the arms, the legs, the heads. Are they too smooth? Too rough? Or just right? (Like the porridge in the tale of the Three Bears?) Do they match each other in casting and surface quality?
10. If the bank looks dirty, check carefully to see if the dirt is old or has the bank been covered with burnt umber, applied to the surface to create the appearance of old patina.
11. Check for cracks and repairs at any of the points where the bank logically would be most likely to be damaged. (The thinnest parts, the edges and corners.)
12. Look for evidence of the paint having aged naturally. Generally you are looking for fine crazing in the paint. This is often easiest to see in the lightest areas. (A small magnifying glass can be helpful to have on hand when looking for natural crazing in paint or small cracks in iron.)
13. Check the interior for repairs to the mechanism. Does anything look new or "too rusty"?
14. Smell the bank and check with a fingernail to see if the paint will take an impression. Old paint does not have the smell of fresh paint and old paint would be dried and not take an impression.
15. Collect the best banks you can afford and make sure you are getting what you are paying for by becoming well informed.