The problem is when someone prophesies and it does not confirm something you already heard from God, and it gives you some kind of direction. You can't say you can sense it is from God, or that it isn't.
As with any prophecy, you have to consider whether it is Biblical. If someone prophesies to a woman to leave her husband and marry him, then we can know that goes against scripture. Of course, that's not a normal thing, fortunately, in church. But let's say you get a prophecy that some day the Lord is going to use you on a missions trip to Africa. If it's some day, you can 'put it on the shelf', and just wait. If it says go right away, you have an issue.
Rather than rejecting prophecies that aren't confirmation out of hand-- which could be an excuse to depise prophecies that seem inconvenient-- we should consider them and make a decision. Some prophecies are given in church. Churches should actually follow, 'Let the prophets speak two or three and let the other judge. If a revelation cometh to one sitting by, let the first hold his peace...' I certainly think it is a good thing when people from the congregation that you trust can say, "I got the same thing." It happens that two people get the same prophecy or revelation, even specific things, at the same time. We need to keep in mind that the early church had a somewhat 'open format' as we see in I Corinthians 14, where believers could use spiritual gifts to edify one another. We don't see the pulpit-pew format in that passage, the passage that goes into detail on what to do at church.
I believe if a church receives a prophecy that is a call to action, it should consider it. The Bible says to let the prophets speak two or three and let the other judge, or some would translate it, weigh carefully what is said. In Acts, Agabus signified by the Spirit that there would be a famine. The church must have evaluated what he said. They decided to send an offering to the poor saints in Judea. The probably knew how a famine would effect the poor saints there.
If it is an individual prophecy, you can seek input from the church especially if it was given in church, seek counsel from the elders of the church, seek counsel from godly individuals. If you are a wife or child you can ask your husband or father. In many cases, the decision is in the hands of the individual who received the prophecy.