Hull blisters are bumps, not indentations. I can't think of what eraser-sized indentations might be, other than partially repaired blisters. They could be the "scars" of blisters that were drained and then never refilled with epoxy/fiberglass. Blistered hulls can be fixed, but it is a royal pain to do yourself, and very expensive to have someone do for you. Either way, it requires a significant investment of time to adequately dry out the blistered areas before making repairs. If you are comfortable working with fiberglass, its not complicated, and because the repairs will never see the light of day and will be covered by bottom paint, you don't need to make it pretty. The level of effort required correlates directly to the number of and size of the blisters. Does the owner know what the indentations are? You can do a search here or on Google to get some detailed information on blister repair.
As for the damaged swing keel, if the rust is significant, you will have to sandblast and epoxy the board. And the pendent cable will have to be replaced. All of your ballast is in that piece of equipment, so I wouldn't screw around with it. All in all, this Catalina 22 sounds like its more trouble than its worth; if your area is anything like here, C-22's are a dime a dozen. If you like the boat (and lots of people love them; I used to have one), then you should be able to find another that is in better shape.
I am less familiar with the Tanzer, but if the boat hasn't been out of the water in four years, I think you can expect significant marine growth on the bottom. If the boat has been in salt water for four years without hauling or bottom paint renewal, I don't see how you would be able to get away with less than a full sandblasting to remove the growth. I don't know of any bottom paint that would protect a hull from barnacles and marine growth for that long. I would insist on hauling the boat before purchase to see and to check the condition of the hull. This owner may be sitting at the dock on the weekends because the boat won't hardly sail due to the bottom being solid barnacles and mussels.
You asked if these were fair prices for these boats; in good condition here in Connecticut, I would say a 1982 C22 in good condition with a trailer would run about 5K. A '76 Tanzer in good shape would probably be about 2-3K. So the prices you have been quoted seem low to me. That means that the market where you are is either significant depressed/different than here, or something is really wrong with these boats. No way to tell from the internet. If you are really concerned, you can always hire a surveyor to check out the boat for you prior to purchase. Make your offer conditional on a successful survey (just like buying a house!).