When I signed with my agency, the contract said that they would make copies of my novel for sending to publishers, and charge me. This is a legitimate up-front fee that most agencies charge.
Their price was 7 cents per page which is fairly standard. Because I know someone in a document company I can however get copies much cheaper even if you include the FedEx charge for my sending them to the agency.
When I asked the agency whether that was okay, they didn't blink. They said they really didn't care who made the copies, but many writers didn't want to go thru the hassle. So my contract has a small paragraph rider about copy making, saying that I will supply copies as an alternate.
But if your prospective agency balks at this, or tries to charge a high per-page fee for copying, it may be another way to spot a scam.