Buying a musical instrument needs to be done with care and if possible with someone who is very adept with the musical instrument you are planning to buy. This is to make sure that you are not wasting your hard-earned money to an instrument with low quality. I remember when Hubby bought his guitar last year. He asked his friend to accompany him to make sure that that the guitar he will be bringing home is of good quality. He learned his lesson when we bought our first guitar without consulting someone who knows what a good guitar is.
There are also some good guidelines which can be found over the net. Just make sure that the author of the guidelines is an expert and knows what he/she is talking about. So whether you are looking for super trumpet mouthpieces or an acoustic guitar or violin or any other musical instrument, you must already have in mind the things that you must consider before paying for the instrument you want to buy.