1 Thessalonians 2:3

For our appeal does not spring from error or impurity or any attempt to deceive, (1 Thessalonians 2:3 -- ESV)

Paul is not shy at all that there is an "appeal" in the Gospel presentation. Paul is appealing to them. He is calling them to a response. The Gospel presentation is not simply to have a pleasant conversation or a feel-good conversation... it is a call that appeals to the very soul of the person hearing this good news. 

Paul clarifies this appeal's roots with three negatives:

1. Not from Error. There is no error or falsehood in this message. 
2. Not from Impurity. This word usually refers to sexual impurity, but it can mean any impurity. So, not just a lack of error in the details, but also in the motivations and meanings of this gospel message. 
3. Not from Deception. And no attempt to deceive anyone. Jesus himself, when presenting the call to follow him, would say, "consider the cost..." or "count the cost..." Nobody is trying to trick you into following Jesus.

Unlike any other charlatans with their shenanigans, Paul (and all true preachers of the gospel) are presenting a straight forward message of the goodness of God in the person of Christ.