Typical book offers range from zero to one hundred thousand dollars. If the prediction is too low, authors begin to lose faith in the agent's professed knowledge about publishing. The size of the advance may not be the most important element of publishing contracts, anyway. Under certain circumstances, the royalty schedule may be more significant than the advance. For example, a high advance coupled with a stingy royalty rate on a successful book may be worse than a low advance and a higher royalty rate.
Most royalty rates are on a sliding scale, escalating as the sales of books increase.
Trade paperback rates are occasionally the same, but usually less. Publishers base their trade paperback royalty rates either on net receipts, rather than list price, or just reduce the royalty rate to about half of hard cover. Again it depends on the publisher. Mail order sales by the publisher have yet another, lower, royalty rate. Every publishing contract has to be scrutinized, and negotiated, to get the best possible royalty schedule.