Sounds like you got a great deal on some really good cookware - and I sure wouldn't take them back! And, yes - the tin lining on good copper cookware is applied by hand.
Yes, you can cook acidic foods like tomato based sauces in them - the tin lining is non-reactive .... that's what it is for.
And, I will stand by my previous statements - threat this cookware with respect - tin is a soft metal - but treat it right and it will last a lifetime. Like Lynnie said, "The tin coating will scratch easily, so you MUST use wooden or plastic utensils. They do heat up incredibly fast." You can't put it on the stove and walk away like you can cast iron ...
As for removing the lacquer - the boiling water and baking soda method sometimes works - lacquer thinner definately does. See here
for discussions on the subject.
Copper does change color when heated ... doesn't mean it's ruined or damagerd - just been heated. Over time - your copper will become darker.