Hello, is there any solid established service with API for domain availability lookups? Or is it unreasonable to expect such service can be free (can be misused..) ?

We need to create software which will need API for this:
a) expiration date check (around 100 daily)
b) domain availability check (like one check every 10 seconds)

someone adviced: http://whoapi.com and that enom.com also works for this