The value would be what it sells for and not what a previous sold price was or what a book says. Prices in today's market fluctuate wildly depending on who is bidding at that point in time, demand, condition, color, pose, maker, age, etc. If you paid 5 pounds and you sell it for 15 pounds, you have made a tidy sum (less fees of course). However, you do have the possibility of it selling for much more, in which case you will have reaped huge profits and elevated you to the status of big oil company profits.
If I could double my money on everything I buy and sell, I would be set for income for life because the money would never run out. However, some things I cannot part with (yet), some things never sell, others are lucky to break even, and the bad ones are losses. The hunt, however, is priceless and fun.
