Many, too much, stamp dealers sell as used  spanish stamps either with:

PUNCH HOLE: Those are telegraphically used and their value is many many times less than those postally canceled. None of this appears on the Scott Catalog.You should  look at the Edifil catalog.

REPAIRED PUNCH HOLE: Some times the punch holed stamps keeps the original circular piece of stamp. These stamps are carefully repaired and regummed, and sold as new ones. Needs a very close look to notice it.

BAR CANCELLED ( HORIZONTAL ONE, TWO OR THREE STRAIGTH BARS). Those are not postally used stamps, but the remains of the production not sold during the year. From 1850 to 1899 all the remains of each year were bar cancelled , and replaced with new designs. Those stamps are also many many times cheaper than the postally used.

PERFINS WITH T1 to T6. They are not perfins,but telegraphically used like the punch holed. Some timews they are sold as new with perfin. The real price is also from 30 to 100 times less than the original new stamp.Be careful.

Nevertheless all of them are a way to get expensive stamps to fill the empty spaces, or to collect apart, or to have a sample of how should look the day you buy a expensive item.

Sorry for my english.