Screens tend to either work or not, if it looks ok with the Laptop on then it is working correctly, just look out for colour blotches on it and try to look at it with a white background, eg an open word doc this will show up any problems.
One thing to look out for is battery, as these tend to degrade after about 18 months and new ones are expensive eg £100 +
Its worth looking about and seeing what model you like and then check up on price of parts, memory etc so that if you want to upgrade then at least you have an idea of costs.