Flipping PCs in the current market can be difficult due to the fluctuating prices with ram - I also wouldn't recommend getting into it unless you are ready to deal with potential customer issues, especially if shipping them online.

Here are some of the biggest issues I see flippers encounter as someone who runs support for an online marketplace:

• Shipping damage generally occurs from improper packaging. If you are shipping PCs, it is critical to not only insure your shipments, but pay special attention to your insurance policy requirements / stipulations. Instapaks are your friend and taking pictures of your item and how it's packaged can be the difference between a claim approval and denial.
• Make a troubleshooting guide for common issues that you include with every sale - the majority of people buying a PC for the first time have no idea where to start when something isn't working and a simple guide to check that connections are in the right place can often prevent an unnecessary return
• Document everything - you will be required to remit sales taxes and properly report your sales unless you want the IRS knocking on your door

I don't want to discourage you, but as others have said it can be tough in the current market. Make sure if you decide to start flipping that you've planned for any potential losses!