That depends. Are you making use of one address for all your transactions? If you have been making use of just one address for all the transaction you have been doing, then they will be able to see all the transactions that you have done so far: which includes all the money that you have received and also the ones you have sent. So that’s for sure that they would see your transactions, And possibly know the balance that you have on that address.  Now if you have noticed, what I was saying here is address, and not wallet: I am using the word address because your address doesn’t necessarily mean that what is stored there is what is  originally stored in your wallet. This can be because when you are making use of a wallet that has different addresses, then nobody would know the actual amount that is in your wallet. So I would advise you to make use of a wallet that would change your address anytime you’re about to make a transaction. That way you wouldn’t have to be repeating the same address all the time.