There are several possible reasons as to why Reverend Parris is unliked in the town of Salem. The first is that his sermons aren't very uplifting or motivating; in fact, as Proctor states in act one, they are pretty much all about "hellfire and damnation," which is a pretty depressing topic to listen to. A lot of the people in the town are farmers who work hard all day long and travel quite a distance to go to church on Sundays. And, to arrive at church, tired, wanting to hear some uplifting and inspiring messages, only to be condemned to Hell and told you are awful, is not a very encouraging thing. It is not only Proctor who feels this; Rebecca Nurse corroborates the claim, adding that "there are many who quail to bring their children" to church because of the intense topics of his sermons.
Another possible reason that people don't like Parris is because he whines about his salary, and strives to gain ownership of the meetinghouse where the church and his residence is. It isn't customary for ministers to own the churches, just because they live on the premises; it is also a bit unusual for a man of God to complain about his salary. In reality, ministers are supposed to be focused elsewhere, not on home ownership or money. Parris is very vocal about his desires too. In act one he complains, "the salary is sixty-six pound," not sixty-pounds with "six pound a year to buy...firewood" as Giles Corey notes. Also, according to Proctor, he works his desire to own the house into his actual sermons--not very tactful. He also preaches of other worldly issues, wanting "golden candlesticks" in the church instead of pewter ones that Francis Nurse made.
One last possible reason that people might not like Parris is because he tends to be a pretty big snob. He claims that he is "a graduate of Harvard College" and not some piddly "preaching farmer with a book" to qualify him for the ministry. He brags of his profitable business in Barbados, and holds airs over the hard-working people of Salem, who sweat and labor for their daily bread. That has got to rub people the wrong way, not to mention that ministers were chosen by election, and there were several other candidates that Parris beat out to the job.
As a result of these issues, Parris is rather unliked in the town; it's hard not to blame them, and understandable why there might be a "party and faction" risen up against him. I hope that these thoughts helped a bit; good luck!