Newly-acquired chubbies often don't want to eat in front of you, so just count the crickets you put in, and check again the next morning to see how many are left.
Chubby frogs are fairly easy to keep.
If you give them some soil or gravel they'll spend most of their time buried up to their eyeballs, and only pop out to eat and at night. At that size, they can climb glass and escape using the little toepads on their front feet. The chubby frogs won't chase the crickets - they'll wait for them to walk past and then nail them with their tongues, which are more than fast enough for the job. Newly-acquired chubbies often don't want to eat in front of you, so just count the crickets you put in, and check again the next morning to see how many are left. Chubby frogs are fairly easy to keep.