I have bought a couple cars in med school and several more in undergrad- No co-signers needed.
Here are 2 experiences in med school:
1. $12,000 car: I told the dealer I was "receiving money" (ie loans-but didn't tell them this) during med school. I said I was receiving 50,000/yr (what my loan stub showed). They did the credit check, I was approved, but the loan company wanted to see my pay stub. I brought in my loan receipt- the manager became a little pissed off because he realized this money is from a loan, but worked it out for me anyways-> they'll do anything to settle a deal!!!
2. $45,000 car (graduation present): I told the dealer I receive $75,000/yr and requested a loan that did not require a pay stub (I said I just moved and threw everything away, and receive pay stubs bi-annually, next one in a few months). Bank One did not require a pay stub with a credit score of 700. Loan was approved by multiple companies and I selected Bank ONe because they did not need proof of work (but I had to increase my interest by 0.2% for this, but still a low APR overall).
They WILL ask your TITLE at work, I said "Acting Intern"- they don't know what the hell that is.
They may call the hospital or med school to verify you "work there". I gave a phone number of a cool clerkship coordinator who said "I work here".
Your APR on your first car financed will be HIGH (>12%) and will get better as you buy more cars later in life. Settle for what you can get if this is your first purchase.
This is not completely dishonest (you are actually "receiving money"), but there is a little fibbing to do (just like they are fibbing with you). And it does work out because they want the deal done! If you go to a desperate Used Car dealer, they will definitely do whatever they can to secure the deal and will BS the loan companies however they can to get the deal done. If you do it over the Internet, there is no dealer to push and call the loan co. for you.
IF this makes you uncomfortable, wait until your 4th year when you can get a "Residency Relocation Loan" at any time during the 4th yr for any purpose, up to $15,000 usually, and use that money to buy.