Hi. I'm not a stamp expert but a dealer may offer you 50% of face value . They will cherry pick anything worth more to a collector and sell the rest as postage stamps at around 75-80% of face. On ebay you can usually buy decimal stamps for postage at around 75% of face value. .  Make sure you know exactly what the face value is before hand... Did you compile the collection yourself or was it given to you? Bottom line , do your homework. cheers.