Sending spends existing outputs; receiving means sharing an address the payer can target. A wallet hides UTXO selection, change outputs, and fee estimation; you still choose whether to require confirmations before crediting a user in your product.
Balance
Use the client’s fetch balance or call fetch_balance on the node API to reconcile with the chain.
Broadcast
After signing, the client submits to the mempool. If submission fails, you get an error in the same envelope the HTTP API returns.