Some trekkers use the services of independent guides rather than checking and finding the right company. If you can identify the right guide for your kind of trekking join with them. Nothing more matters on the trekking route than having a trustworthy and experienced guide with you all the way.
Some of the things to ask your self and consider before hiring a trekking guide are
Do they have adequate knowledge about the weather and route of the region.
Are the guides registered or not. If they are not then you may have problem getting the permits.
Do they speak and communicate well with you in your language? Communicating well with your guide is very important.
Do they speak and understand English?
Do they have first aid training? In case of some accidents, wear and tear.
A little bit of research and common sense goes a long way.
One thing of advice to keep in mind is be careful when making payment to guides. It is a good idea not pay them in full in advance.