Basically: Purposely NOT doing whats legally or ethically obligated or entering an agreement with the intent to deceive or not fulfill obligation.
So again I am a LAYMAN
Are you NOT legally response to get your client the BEST deal?
and also REVEAL any potential bias or impropriety?
Is THAT not deceptive?
Is not giving ONE client a weaker deal to benefit ANOTHER unethical?
Is a lawyer not obligated to do the BEST job possible for their client?