maintenance of books

Nope, person doing business and generating an revenue or gross receipts less than 10 lakhs no need to maintain the books of Accounts

how you will decide that your gross receipts is less than 1000000/- with out maintaining books

There is no requirement to maintain books of accounts.But if u wish u can

requirements are different... without books how one would able to ascertain his total income or gross receipts?

Basis on Bank statement transactions

bank statements are also part of books only. how will you ascertain cash sales

It means it is the duty of a business men to maintain the proper accounts, If he doesn't, Auditor or Consultant will take the income basis on Bank statement.

He might be dealing the transaction with his client through bank, just in case we can't say it as a books of accounts.

It is kind of Inflow and outflow, in Inflow he might be deposited cash and he might taken loan from third party, but for Income tax they doesn't mind it, basis on overall gross receipts we have to calculate net income.