Keep in mind that you may not know who has used it or where it has been and you are going to stick it in your mouth.
The first thing you need to do is get it cleaned and serviced. You can and will catch cold germs/mouth ulcers and even gastro from a second hand instrument, particularly woodwind instruments need a clean and bath at least once a year.
If you are hiring an instrument, you need to know if it has been cleaned and disinfected.
If you're not sure, take it to a repairer. Don't trust the hire company!
Coughs and colds do live inside instruments and every time you stick it in your mouth, you are continually going to risk infection. School Instruments generally get handed from one child to another every year with little thought and consideration to cleanliness and hygiene.
It is not until the instrument needs a repair that it might get a clean. Due to repair costs and budgetary constraints the O.H & S get forgotten about. You wouldn't give your child somebody else's left over food, so would you give them somebody else's left over instrument? The relevant health and safety authorities do not take any interest in this area (having already canvassed them myself). This is why I need to bring to your attention as a consumer entering in this activity.
You need to find a repairer who is a musician in this field of expertise and has a good reputation as a repairer. Ask around friends and other muso's for references, then call the repair and ask "What do you get for your money?".
BEWARE: Some repairers charge like wounded bulls, so ring around and get a quote up front or ask for a second opinion. You don't need to pay the earth for quality servicing. Use my repair schedule as a guide to what you may expect to pay.
You will be shown how to clean your instrument, learn the importance of maintenance and caring for your instrument. If regular services are over looked, the functionality will deteriorate resulting in excessive wear and tear and dramatic reduction in the life of the instrument.
Some teachers unfortunately do not consider it their job to teach students about maintenance. Oiling an instrument should be done regularly to stop rattles and squeaks, and also reduces wear and tear.
I see a lot of instruments that have obviously never had a proper clean and just a repair has been carried out. This is only half of the job. Keeping your instrument clean and germ free is as important as keeping it in good playing order. Clarinet, saxes, flutes, trumpets etc, all harbour bugs, grime and diseases. Considering we all get coughs and colds, we eat and drink sticky drinks and food which then get sprayed down our instruments when we play. It's a good idea to wash your mouth out before you play an instrument as food particles get stuck between your teeth. Playing somebody else's instrument is not particularly hygienic to do.