The mere fact of signing up for a developer account with eBay gets you access to both sandbox and production environment.
Without lifting a finger you get 5,000 production API calls to eBay for your application. No approvals or anything needed to have these 5,000.
By the way this is 5,000 per day.
If you want a need more then you'll have to submit your app for compatibility check by eBay.This is basically to ensure their TOS and best use of API for your objective is being used. Once approved, they will increase the call limit based on your needs.
The application application isn't hard to pass. I've had simple 5 pages of code passed and more complex apps passed. In fact I've never failed an application check before.
Make sure to include in your application check why you need higher limits based on use now or in future. If you don't ask they might not give them.
PS - If I recall , I never even actually had to submit my application (actual software file) to eBay for compatibility check. Just took screen shots of application and documented what it would be used for, who would use it and what API calls we were using.
I was initially given 1 million API calls a day and upon a simple request was able to increase it to 2 million without any fuss.
Lastly, I would note that if this application is for internal use only, then make sure to tell them that because if you plan on collecting user credentials then eBay would surely require some more advanced checking. All my apps previously did not collect credentials or require them. Just used the finding API.
Just be legit and not doing anything funny and eBay will support all your needs in regards to using their API and increased call limits no matter if your small fish or enterprise.
UPDATE
Default now seems to be 1.5 Million calls as soon as your app passes Compatibility check.
When applying, their major concerns are related to error handling. Ex: If call fails, you have some method to either report it in a log file or take action to resolve/terminate. My last app was successfully approved with a simple log tab that reported any API errors on the UI and stored them into a CSV file local to the machine the app was installed on.
They're not looking to approve based on your apps ingenuity, rather just trying to prevent abuse.
