It's not as clear cut as you (or others) may think.
As per the various copyright and distribution laws, AND industry service regulations AND the DMCA and the legal rulings in induvidual states striking down the DMCA....
As a buyer:
You have the right to "safeguard a product you own"
You have the right to "protect your investment"
You have the right, under the Distribution of Rental Materials act to watch an item (VHS/LD/VCD) you have legally rented (the act does not cover DVDs, so it's a craps-shoot in the courts to this day), and to use reasonable means to enable the watching of such rental items.
For the time being; you have the right to make an informed decision of intentions to purchase an item of dispensable media (used to justify downloads for x number of hours), which has been both struck down and upheld in different cases
You have the right to guarantee compatibility with your [system] if your purchased item claimed to be compatibility (ie the DVD symbol or the DVD term on a box) and you made a "reasonable" assumption of compatibility : and to enforce said compatibility on [said system] if through "no fault of your own" your disc is not compatible with your [player]. (Has been both upheld and struck down as for a legal use of "DVD Decrypter, AnyDVD...et al).
As for a backup service, first of all you MUST have at the very least a state business licence (easy to get and often free) to legally make a backup of anything. Rules vary from state to state.
You have the right as a business/service provider to conduct the process of making a 1:1 copy, OR an "improved quality" copy of any media if:
You have "reasonably assessed" the legal right of the product owner to make such a backup on their own,
AND you can "reasonably deduce that the owner could not make" such a backup on their own
AND that the owner "is the legal and rightful owner" of that particular item
OR that that owner is the "First owner of a [particular] media" item.
Confused yet?
In short: the burden of proof of legality of the owner holding an original and true copy falls on you, for 30-365 days depending on the state. So YES you COULD make a backup for someone without receiving the original if both you and the holder have the EXACT same disc (as I've posted before, there are varying versions of media even from different STORES), and even then you're still taking a gamble. You're best asking to have the original sent to you and copying that.
:note: I'm not an licensed attorney, I only have a legal practitioners' licence. If you plan to do this; I'd suggest you hire an ATTORNEY to discuss the various legal ins and outs of the system as it stands, and as it changes. You can usually get one for a decent rate by going to a major university and talking to a Law Professor. They could refer you to recent students, and tend to only point you to the better ones to protect the school's reputation. Fresh law grads tend to have lower fees for school-based referrals.