One may argue that since Śaṅkarācārya is an incarnation of Lord Śiva, how is it that he cheated people in this way? The answer is that he did so on the order of his master, the Supreme Personality of Godhead. This is confirmed in the Padma Purāṇa, in the words of Lord Śiva himself:
māyāvādam asac chāstraṁ pracchannaṁ bauddham ucyate
mayaiva kalpitaṁ devi kalau brāhmaṇa-rūpiṇā
brahmaṇaś cāparaṁ rūpaṁ nirguṇaṁ vakṣyate mayā
sarva-svaṁ jagato ’py asya mohanārthaṁ kalau yuge
vedānte tu mahā-śāstre māyāvādam avaidikam
mayaiva vakṣyate devi jagatāṁ nāśa-kāraṇāt
"The Māyāvāda philosophy," Lord Śiva informed his wife Pārvatī, "is impious (asac chāstra). It is covered Buddhism. My dear Pārvatī, in Kali-yuga I assume the form of a brāhmaṇa and teach this imagined Māyāvāda philosophy. In order to cheat the atheists, I describe the Supreme Personality of Godhead to be without form and without qualities. Similarly, in explaining Vedānta I describe the same Māyāvāda philosophy in order to mislead the entire population toward atheism by denying the personal form of the Lord." In the Śiva Purāṇa the Supreme Personality of Godhead told Lord Śiva:

dvāparādau yuge bhūtvā kalayā mānuṣādiṣu
svāgamaiḥ kalpitais tvaṁ ca janān mad-vimukhān kuru
"In Kali-yuga, mislead the people in general by propounding imaginary meanings for the Vedas to bewilder them." These are the descriptions of the Purāṇas.

(SRI CAITANYA CARITAMRTA-------1:7:110-------PURPORT).