Many companies provide auto dealer software solutions nowadays. Dealer management systems (DMS) and website integration make a huge impact for the success of your business.
Purchasing: Most used car dealers purchase their inventory from auctions. Your DMS should help you with that. You should be able to enter how much you spent on floor planning, auction fees, transportation, etc. Same thing goes for trades. You should be able to enter a trade at the time of a sale. When you enter a vehicle twice, you risk making mistakes. After you purchase a car, you should be able to track how much you spend on reconditioning.
Marketing: Online marketing has changed the way dealers do business. You have to have a website these days - no matter how small you are. You need to be able to list your inventory in your website as well as publishing news and specials. Your website is your virtual lot. It does not have to be head turner but perform well in search engines and fulfill its purpose: marketing. Your automotive dealer management system should be integrated with your website. Preferably, it should be the same system. In order to get the real power of Internet, you need to post your vehicles to 4 places: Autotrader, cars.com, Craigslist and eBay Motors. You should be able to do that from your DMS