It doesn't seem to mention how you know, when someone claims to send you X BUCC, how much BUCC you actually received?
There are "Decrypt" and "Partial Decrypt" functions in the dapp (note this will issue a transaction) under Tortuga which reveal your balance.
Running Decrypt will deanonymize any private balance you have (so only run it if you don’t remember/know what balance you have).
Partial Decrypt will deanonymize any smaller balance you input that is smaller than your total private balance.