If you are unhappy with the offer its best not to accept it. Find a place that offers a reasonable offer. I would then contact the clinic or hospital, ask to speak to a dentist who works there of the same nationality (yes, passports speak louder than experience) and inquire about what it is like to work there (maybe swap emails). They will give you the true work hours, pay, benefits etc. so your not given a false idea of your new company (it does happen!). As you said, if you make the mistake of choosing the wrong company first you usually dont get a second chance in Qatar (or have the time to wait for one - 2 years or more)!
If you are unhappy with the offer its best not to accept it. Find a place that offers a reasonable offer. I would then contact the clinic or hospital, ask to speak to a dentist who works there of the same nationality (yes, passports speak louder than experience) and inquire about what it is like to work there (maybe swap emails). They will give you the true work hours, pay, benefits etc. so your not given a false idea of your new company (it does happen!). As you said, if you make the mistake of choosing the wrong company first you usually dont get a second chance in Qatar (or have the time to wait for one - 2 years or more)!