"My husband has bought some online for 60 or 70% of face value."
That was a great deal.
Typically, at public philatelic auctions, mixed lots (face value $1,000 to $10,000) sell for 60% to 70% (before tax) after considering the buyer's premium, assuming no premium stamps were included in the lot.
Lots made of low values only ($0.04 to $0.10) sell for about half face value as nobody really wants them.
Lots with high values stamps only ($1.00 to $8.00) generally sell for more (about 85% of face value).
That is based on mint Canadian postage stamps with full original gum. Lots offering uncancelled stamps without gum (50% to 75% below face) should be avoided . It is illegal in Canada to re-use an uncancelled stamp that has already gone through the mail without being cancelled.