All it takes to prevent a bad purchase is to ask yourself a few questions and answer them honestly. In this age of consumerism, pseudo "justifications" can empty your wallet pretty quickly. So before you make a purchase, asking yourself these three questions might save you from making a bad purchase.
1) Is this a necessity or a want? If not buying it will negatively affect your lifestyle, then its a necessity. If it is, think it through and tell yourself whether you have done a thorough price comparison with similar items. If it is a want, ask yourself whether you can delay it.
2) Is it worth foregoing a chunk of your investment money to buy this? Big ticket items will usually dig into your bank reserve/investments which are actively collecting interest. Do you love this item so much that you are willing to forego precious interest for it? ......