Expect to take on more risk than normal when shipping records. Some will break, it is just inevitable. Don't let USPS tell you you have to use any form of shipping other than Media Mail (unless you specifically want priority, etc). Don't bother shipping a record unless it is worth $10 or more. Of course that is my opinion. Condition is 1000% everything with records. Grade conservatively. You will get burned if you advertise a scratched up record as "mint". If you do not know what you are doing, you are better off not using any grade above VG+ even if it looks unplayed. VG is considered average played grade and allows for some (non major) flaws. Messed up records would automatically be in the G range or worse. No one buys records below G. Serious record collectors will be very cautious/suspicious when buying a record graded as "Mint". If a sleeve has visible mold, throw it away unless it is extremely rare/valuable.
IMO, country 45s from the 60's/70's sounds like a losing proposition.