Great question, and I think different attorneys will differ. If it's a single sale, probably not. If it is a continuing series of sales, probably yes. I suggest that given the very low cost it is well worth it since if checks do arrive to your eBay fictitious name, you won't be going back and forth on the payment issue.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
I would suggest having a fictitious name for doing business purposes, though there is no legal requirement that you do. It would be useful to have the fictitious name to help you with your acounting. You should be able to do the filing yourself, or may hire an attorney if you do not feel comfortable. You begin by making sure the name is available. On you browser, enter "name search PA corporations bureau". This should take you Pennsylvania's Department of State, Corporations Bureau and a screen where you type in the name of your fictitious name and see if anyone else is using it. If not, then go to www.dos.state.pa.us/corps which will take you to a page that that says "Forms" on the left side of the page. Click on "FORMS". This will take you directly to the Fictitious Name form to be filed. The instructions for the form are included. It costs $70 to file The form says it should be typwritten, but It is not a problem to fill it out with a black pen, assuming your printing is neat. Then, make sure the post office knows of the new name for your address. Please call me if you have any questions. I may be reached at 610-296-1985. Good luck!
In many if not most cases, a bank will not honor a check made payable to a DBA unless that DBA is registered. So you will be stuck with checks you cannot cash if you do not register your DBA or fictitious name as made possible under PA law.
Licensed in Maryland with offices in Maryland and Oregon. Information here is general, does not create a lawyer-client relationship, and is not a substitute for consulting with an experienced attorney on the specifics of your situation.
Attorney Marcus is right. I know my bank requires a dba filing to set up an account. They want assurance you are the payee and will not necessarily take your word for it, especially if they have ever been stuck to due cashing of dba checks by other than the party who has the dba filing.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.