First, pray over your decision and ask the Lord for peace about the decision. Next, ask advice from a number of people whom you trust before making the purchase. Remember, in the multitude of counselors there is safety.
Next, avoid impulse decisions by waiting on the Lord for clear direction. Failure to wait appropriately basically doesn't give the Lord any opportunity to provide real peace about the decision.
Also, always be sensitive to the clear statements of Scripture concerning your decision. Never make a decision that violates Scripture. This is another reason for an appropriate waiting period. As you couple the Scriptures with your prayer over the matter it gives the Lord an opportunity to impart wisdom and guide you to HIs best regarding the decision.
Every believer should desire to be a faithful steward of the resources the Lord entrusts to their care. Purchasing decisions that hinder faithful stewardship should be avoided.
Perhaps the information found in this article will help you in some way to be a more faithful steward.