For me it's a balance between price, avilability (Geographic Restrictions), continuity (Jean M. Auels "Earth Children" series can only be bought as (e)book 1, 2 and 5), and "must-have".
I'd really like to buy "The Clan of the Cave Bear" but since there will be a hole in the continuity, i.e missing book 4 and 5, I skip the hole series. And yes, I'm willing to pay the price (for Europeans) of US$ 10,97 per ebook. Too bad Jean, you lost this sale d.t missing books.
Most of my pbooks, I do not rebuy, although there are exceptions, such as the galactic survival guide (The Ultiate Hitchhikers guide to the Galaxy by Doublas Adams) and a few reference books.
"Must-Have"'s are likely books by Ken Follett, Dean Koontz and Clive Cussler, for which the price is the *last* criterion.
