"Investment banks" create loan agreements that cater to the needs of the investors whose funds they attempt to attract; "investors" are always sophisticated and accredited organizations not subject to bank regulatory supervision and the need to cater to the public trust. Investment banking activities are supervised by the SEC and their main focus is on whether the correct or proper disclosures are made to the parties who provide the funds.
The interest rate for these types of loans is plus 1 percent of prime and is adjusted monthly. For these types of loans, borrowers are completely responsible for all third party costs and points can be bought with these types of loans to keep long term costs down.
Prior to entering into a loan agreement, the "borrower" first makes representations about his affairs surrounding his character, creditworthiness, cashflow, and any collateral that he may have available to pledge as security for a loan. These representations are taken into consideration and the lender then determines under what conditions (terms), if any, they are prepared to advance money.
It is an unsaid rule in the world of loans that one needs a co-signer to ensure that the student loan gets approved. That said, it does not mean that you would not get loans if you do not have a co-signer to sign on your agreement. There are some lenders in the market who would offer loans to you with you having to worry about the co-signer.