First of all you have to decide what you need it for. If you are wanting something that will do what it says on the tin and nothing else then have a look on eBay for a second hand - two channel mixer (allows the user to mix two live lines of music simultaneously). You should be able to pick one up for under £40 and it will work straight away with your turntables or whatever you use. Take a look at Numark or Gemini. They seem to produce the best quality budget mixers.
If you have had some mixing experience and would like something that will allow you to progress then i would not recommend buying something that is bottom of the range. I would recommend buying something which ideally has 4 channels to allow you to upgrade to both vinyl and cd at a later stage without having to buy a new mixer. If you have your heart set on buying a two channel mixer then you are still spoilt for choice as plenty of companies offer great quality mixers which have 2 channels. Some mixers are 3 channel which make them a cross between the two. Take a look at the vestax vmc180. At less than £200 new it could be an option for all budding dj's.
If you have been mixing for years, or maybe just believe that you have a real talent perhaps you should be looking at some of the high end gear. Most of it is made by pioneer and if you want real sound quality, my advise is not to go for anything which is less than £250. If you are considering this then I suppose you will not have to read this guide as you will already have your own knowledge.
What to look for
If you are buying a new mixer then just look to see if the seller has good feedback and that the price is right! If the seller does not have 100% feedback then look at their feedback by clicking the number by their name and look to see what the people who left negative have to say. There can be nothing wrong with anything that is sold as brand new so look to see if the seller has a returns policy or if it includes manufacturer warranty because you could be being sold a faulty item.
If you are buying second hand then still look to see what the buyers feedback score is however there are more important things to do that are specifically to do with mixers that you should check for. Ask the seller what the sockets at the back are like. If they are scratched up then it is more than likely that it has been used in many different places and leads have been in and out of the sockets many times. If the sockets still show unscratched silver then it is likely that the mixer really was used for bedroom use as it shows little signs of being moved around.
Ask the seller what the faders are like, if they are stiff or too loose. If either side of the crossfader looks too scratched compared to the other side then it is more than likely the mixer has been used for scratching meaning that the crossfader has endured heavy use and may break soon so take a look at how much a replacement for that specific mixer is.
OBVIOUSLY read the listing carefully as you should do with all auctions. Sometimes the item will come with a big surprise such as no box, missing fader grips ect. If it does not state this in the auction or pictures then as a buyer you can make a claim for your money back and the seller will have to pay the return postage.
I hope this has been of good use to you, more DJ guides coming soon!