I have a lot of experience in this, and unless you are dealing with an unethical domestic firm or a place overseas, a fax of the prescription and a follow up call to your doctor will be required.
Buying prescriptions online can be cheaper sometimes if you buy your three month supply at one time. You may have a three month supply if your script is for 1 month and can be refilled three times.
Yes they check to see what the prescription is for because they can face severe federal fines, prison time, or loss of their license if they knowlingly dispense Scheduled Narcotics to someone without a prescription.
If you need more information PM me.