1. A method for determining an optimal availability outlook database refresh rate, comprising: simulating a shopping system that includes at least one simulated availability outlook database, the simulating including updating the at least one simulated database in accordance with a database refresh rate; repeating the simulating for each of a number of database refresh rates; calculating error rates for availability of products resulting from each of the simulations; estimating customer satisfaction levels for the error rates; and determining the optimal database refresh rate by comparing the customer satisfaction levels to corresponding costs of implementing database refreshes for each of the database refresh rates.