What to look for when buying a horse trailer?

When you are looking at buying a horse trailer make sure you know what you want out of it. 
What payload capacity are you needing? 
How many horses will you need to transport at once? 
What height are your horses? 
Do you horses prefer to travel forwards, backwards or herringbone? 
What accessories might you need? 
What security products might you need? 
Do you need somewhere to transport tack? 
What insurance is best for your needs?