Most functions are one-off's, so you want to make sure you get it right. These tips are in no particular order of importance, but all should be considered.
First, before you even contact a mobile disco company, it's vital that you don't have your mind on hiring the cheapest you can find. As in most things, you generally get what you pay for. especially with a one off event like a wedding, don't you want the very best you can possibly afford?  Let's face it, in a week or two, most of your guests won't remember what food they had, what the flowers looked like, how great the cake looked or how the room was decorated... But ask them if they had fun, and I'll bet they'll remember, and who do you think carries the can for that? Damn right, the DJ.

If you're paying £300 plus for the wedding cake, god knows how much on flowers etc, why would you expect to pay less than a few hundred quid for a professional DJ? But we're getting caught up with the wedding thing, when we're just trying to find a good DJ for you. Ok, let's face it, there's no substitute for a word of mouth recommendation. However, make sure the person recommending hired a DJ for a similar function to the one you're about to organise.  The DJ's approach for an 18th birthday is, or should be markedly different to the approach for a wedding reception - and you thought we just turned up and pressed a few buttons?

Next, if you call a DJ and he gives you a price without asking any questions about your event, that should set off warning lights.  Questions a professional DJ should be asking include:

• Type of function - Wedding, birthday, kids party etc
• Venue
• Number of guests
• Start and finish times
• Particular music requirements - no point hiring a Rock 'N' Roll DJ for an 80's theme night
• Access to venue.

Ok, this one might seem obvious, but make sure the company you're dealing with confirms everything in writing and that they have a written Booking Agreement for you to sign.  The Booking Agreement should lay out all details of the function - date, venue, times, overtime rates etc.  This Agreement is to protect both the company and the customer and should not be heavily biased in any one party's favour.
Does the mobile DJ have back-up equipment in the unlikely event that anything packs in on the night?  
I say unlikely,  if they're professional they'll use pro equipment and this tends to be very sturdy and not given to blowing up at a moment's notice. 
However, a less than professional DJ, the kind that are just in it for the beer money use very substandard equipment, even, I hate to say CD players you'd find in your average home hifi system.  What happens if the DJ is taken ill on or before the date of your event?  Do they have a plan for making sure another suitable DJ will do the job? 

While we're on the subject of mobile disco companies using other DJ's... Is the person your dealing with, either on the phone or via the company website the person who will be doing the actual DJing on the night?
When someone calls The NRG Roadshow, they are talking to me, Nick Lomath & I will discuss all requirements with you from the point of initial contact right through to the time of your event. I'm also only ever a phonecall/email away should you need to contact me for any reason.
If we're not available on a particular date, we won't take the booking and then act as an agent for another DJ -- you deserve better treatment.  How many shows does the company send out on any one night?  If a company sends out 4 shows on a particular Saturday night, there's a 75% chance you won't get the DJ you spoke to when booking, this will not happen when you book The NRG Roadshow 

 If you need a gas engineer, legally they have to be CORGI registered to do any work, there is no such legal body set up to protect you when hiring a DJ, so when dealing with a company that have multiple shows, how do you know the guy that turns up is going to be suitable? Answer, you don't!
Thats why when you book the NRG Roadshow it will be us and DJ Nick Lomath that performs at your event to make sure you have a fantastic night of dancing and fun!

A quick word about mobile DJ websites... If you're browsing the internet for a professional mobile disco service, you can tell a lot from a company's website.

• Is it simple to navigate
• Is the information clear and simple to understand
• How's the spelling and grammar
• Do they make it a no brainer in terms of booking them.

All minor points, but a sloppily designed website could be an indication of a less than professional outfit.

Ok, some very quick things to bear in mind...

• Does the person you're speaking with seem enthusiastic and knowledgeable about their work?
• Do they appear to be listening attentively to your requirements and asking appropriate questions?
• Do you get good vibes from the company?
• Can they put you in touch with previously satisfied customers?

In closing, please do not skimp on price... Any professional who meets all the above criteria won't come cheap, and I wouldn't hire them if they did.
Price can depend on location and the type of event but don't expect to pay less than £200 for a 4 to 5 hour show.
Any less than £200 and I'd be seriously concerned that they weren't entirely legal.
It costs a lot of money to keep a mobile disco on the road.

Remember what I said at the start? The entertainment you hire will be the thing that the majority of your guests will remember most, and it works both positive and negative. Get it right when hiring your mobile disco and the wonderful memories will last a lifetime.