second hand is good but if its a modern pan you wont need to sand it.  take your new pan and dump about half a centimetre of salt in it and then heat the fucker up until it smokes and then throw the salt and wipe it out, itll draw any moisture out of the metals pores.  then just lube it up with lard and heat again, keep doing that until the fat stops soaking in and youre good to go. youre essentially creating almost a polymer coating.  if thats too much hassle just get an enamelled pan.
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