The quick answer is; You get what you pay for. To expand on that... Cheap DJs are cheap for a reason. They are most likely amateurs just getting started in the business, and have not properly valued their services. You may think that is great for you, because you get off cheap. But a DJ who undercharges will not have the available capital to invest in the upkeep, and upgrading of their equipment, and probably won't have professional quality equipment; and instead will have to use budget equipment that is not meant for large crowds, sounds sub-par, and is prone to failures(wireless mics that cut in and out, hissing or buzzing form PA systems, inconsistent volume levels, or sound that is muffled, or unclear to name a few). It is also simple economics that businesses with an unsustainable model don't last. So that $300 DJ may seem like a bargain in january, but when they are out of business in June and you are frantically searching for(and paying) a replacement, the value tends to fade.
No. DJing is my full-time vocation. It is a labor of love, and I am very thankful I can make a living, and support my family doing what I was born to do. This is a fact you should consider heavily when booking any DJ. Since DJing is my sole source of income, I have no choice but to use the highest quality equipment my budget will allow, put forth a professional demeanor, and appearance, and absolutely blow the roof off of every event I step foot in. As a business owner in a connected world, I live and die by my reviews and reputation. Whereas a part-time DJ who has a day job to fall back on, and who just plays weddings for "extra cash", can completely ruin your big day on Saturday, and walk right back into his "real job" on Monday morning, chalk it up as experience, and be unaffected. I on the other hand would suffer. I have all my eggs in the DJ basket, and though I have a lot of fun doing it, I take it just as serious as any other professional would their career. If I don't please my clients, I don't perform; and if I don't perform, I don't eat.
There is a lot that goes into successfully DJing and MCing a wedding, First and foremost is experience, having performed at hundreds of weddings over the years I have seen, or been in just about every situation imaginable(good and bad), and have the experience necessary to identify possible issues before they arise. A good example of this is; imagine you and your newly betrothed are called up to the cake cutting table at your reception, for the traditional cake cutting ceremony in front of all of your guests. The announcement has been made, the perfect song you selected is playing, the photographer is snapping away, all eyes are on you...and someone forgot to put the plates, cake knife and pie shovel on the table. This is where my role as MC, or master of ceremonies comes in. Once your reception begins, I take the reins and run the show, and ensure those details don't get overlooked. I am constantly aware of where we are in the timeline, what event is next, how long each event, dance and formality will typically take, the mood and energy of the crowd, the lighting and volume levels, the temperature in the room, and yes; even the little details like your cake knife. Because all of these details matter, and something as seemingly insignificant as sending the catering staff scrambling for cutlery while you stand there waiting can make your big day come off as awkward and amateurish. 2 words that you never want associated with your wedding.
It's true, I do make the occasional misstep. However it is normally something most would consider insignificant, but on the rare occasion something that could impact you or your guests enjoyment of the evening occurs I have probably dealt with that same issue in the past, and have the experience to professionally and gracefully smooth the waters and move on; and always travel with redundant backup equipment for all essential gear, in the event that technical failure is the issue.
I have a co-op of other professional DJs in the region who take turns acting as back-ups for one another using a round-robin system. These are 4 other DJs for whom I vouch, and who are also all great wedding DJs in their own right.
I have an online wedding planning system, that allows you to plan your big day right down to the last detail. My music selection system will allow you to listen to previews of the songs you are considering, make notes(such as "begin the song at 1:36 instead of from the start"), gives you suggestions for your special dances and formalities, has a do-not-play list, a special link you can share with your guests in the weeks leading up to your big day that allows each guest to select 2 songs each to be played during open dance, and even has Spotify integration, so you can import your favorite playlists directly from your Spotify account. The planning system has a drag and drop timeline generator, so you can set the order and timing of each event, a names form for your bridal party and immediate family(I use this during your grand entrance at the reception to announce your bridal party as they enter), and another form with basic logistic information such as the venue address, dinner style, etc.