Firt of all, if the pastor is a completely vocational pastor, it is only right to make sure that the salary is sufficient to live on. In the case of a bi-vocational pastor, the pastor's other income can be taken into account.
Many people think that pastors should not be paid, but if we are talking about the decision being made by a church that follows the Bible, then they should follow what the Bible says on the matter. Some point to 1 Corinthians 9 as indicating that Paul did not take pay for preaching, and that therefore, it is not God's will that we have a paid clergy. But even a casual reading of that chapter will reveal otherwise. Verse 14 declares, "In the same way, the Lord has commanded that those who preach the Gospel should receive their living from the Gospel." It cannot be asserted that Paul's relinquishing of his right to earning a living from the Gospel countermands a command from God, and Paul's statements in the chapter make it clear that Paul knew he was entitled to this pay, but chose not to take it. If the clergy are to make their living from the Gospel, then a living it must be. A guide for an appropriate level of pay might begin with the mean salary of the parishioners whom the pastor serves. I do think that it is ok to consider the level of education and experience as well as the on-call nature of the ministry when setting a salary. I do not believe that the size of the church should necessarily be taken into account, as those who shepherd huge churches might well earn lavish salaries, not commenserate with the needs of a pastor and his family. But neither should they be impoverished and at the mercy of a stingy congregation who can afford to pay a living wage.
Ultimately, the congregation should realize that it is God to whom they will answer, whether it is for failing to pay the workman his wages (1 Tim 5) or for wasting God's money on extravegant salaries.