If you have never played the flute then the most important this is to talk to a professional teacher first, BEFORE, you go out and buy the first instrument you see. There are many different makes and models of flute and not all are suitable for a beginner. Ask advice and if possible get them to come with you whislt you choose. The best advice is to stick to well known, reliable makes which have a proven track record. Be wary of "deals" as many are quite often not the bargain they seem so always consult a professional!
Most players who reach the higher grades, find that the pieces they are playing require a variation in tone colour and quickness of response that may be difficult to achieve on their student instrument. The "step-up" and intermediate instruments are the usual solution to this situation.
Many players who test instruments tend to spend time playing through pieces. Although this can be to some benifit, it usually means that the player is not stretching the capabilities of the instrument. Long, held notes and scales are usually the best way to test the tonal qualities and tuning of a flute; bend of notes and leaping between octaves test the flexability. Pianissimo top register notes and fortissimo bottom notes test the dynamic capabilities. In addition you should try any technical difficulties you find hard on your existing instrument. Only after trying these techniques should you think of playing pieces, even then only ones you know very well (otherwise ll you're testing is your sight-reading ability).

Mon - Fri: 0930-1730
Saturday: 1000-1700
Sunday & Bank Holidays: Closed