How can I get a list of all the items for a seller?
For large volume sellers, you may want to consider the following options:
If the seller has a store and all of the items are of the type StoresFixedPrice, then consider using a listing feed.
The other alternate is to use FileExchange and create a Download Report.
For both these options, the seller will need to do the setup.
If neither of these options can be used, then you need to use GetSellerList. If you do not need all the information, consider using a GranularityLevel of Coarse in the call to make your application efficient.