Sales engineers have to be good enough to bluff their way through the layers of hyperbole/minor exaggeration/utter bullshit (delete as applicable) the sales team have spun. Whether their conscience gets involved before the deal closes, different question.
Not at my work. Around here sales engineers just say "this is a proof of concept, X will be different in the final version". Then, after they close the deal, they give us their half implemented feature they developed that none of us heard about before, and tell ys that we need to finish it and include it in the next release.