*Some exceptions apply, for gods of trickery and deceit, such as Shar or Mask.

How would you play a cleric that's dogma strictly says be deceitful?

Spread lies, misdirection and misinformation. There have been some amazing Clerics of Cyric about, and some that you wouldn't have guessed.

It really depends on the deity, but you can't just go around lying to everyone all the time. What I mean by that is you still have to actively pursue the goals of any clergy for any faith, which are 1) Upholding the dogma (in this particular case, spreading and propogating lies, deceit, etc as 9lives said. 2) You do need to gather and convert people to your little secret society and make them do evil things too. You can not be an evil cleric of an evil god without doing and promoting evil.

Not all clerics that lie are evil, stop assuming this :)

Not all clerics that lie are evil, stop assuming this

While your statement is correct, it also holds for any non cleric that lies as well. The dicussion was not about "cleric that lies" = "must be evil", as that is a narrow view of what I had stated. Rather it was about "Gods who a) actively promotes lying, trickery and deceit, and who are b) evil" = "must have clerics who promote their dogma". This was implied by the examples of the Gods you referenced (Shar and Mask), who represent some of the evil gods, who have these aspects within their portfolio.

Other Gods of trickery (halfling and gnome LG-CG deities for example) focus on a wholly different aspect of that domain, for example: practical jokes, trickery vs your enemy, etc...while the malignant deities are focused on trickery to spread strife, misery, suffering, and woe. Yes, trickery in and of itself is not evil. But if you are a cleric following the dogma of an evil god, the results of that trickery will be to spread evil.