The biggest obstacle to becoming successful as an eBay seller is branding. You do have the advantage of operating under the eBay brand, which is substantial – but your ultimate goal shouldn't be to have your customers say, "I bought it off of eBay." Your goal should be to have your customers recognize and appreciate your own brand. EBay is just a selling tool, don't make the mistake of relying too heavily on eBay for driving your sales.
You are Your Own Business
You're starting a business of your own -- you're not eBay. The most important part of that process is establishing your own brand and your own identity, and so your company name – reflected in your eBay user ID – is going to set the tone for your future success.
A Name that Works Outside of eBay
The best eBay sellers don't limit themselves to selling on eBay exclusively. You may want to create your own sales website outside of eBay to complement your eBay sales efforts, and your off-eBay identity should match up with your eBay user ID. Keep in mind that your identity should be reflected everywhere – eBay, your own website and domain name, your Facebook and other social media presences, and in any print collateral you may create. Selecting a eBay user ID is not a step that should be taken lightly. This will establish your relationship with your customers, and make it easier for them to identify you from a very crowded marketplace.
Trends in Company Names
You're not just choosing a user ID, you are choosing an identity -- a name for your company. Advertising professionals are very good at that, but short of bringing in the heavy hitters from Madison Avenue, it is possible to choose an identity on your own with a few things in mind. Some of the biggest trends in branding and identity involve using made-up or misspelled words. Think of company names like "Skype" and "Zynga" for example – these are completely fabricated words that have no meaning whatsoever. Also, misspelling a word may make a brand stand out more, as is the case with companies like "Tumblr" and "Digg." If you do have a marketing budget, consider bringing in a marketing expert with a specialty in naming.
Stand Out from the Crowd
Choosing a unique name is essential on two fronts: First of all, you want to make sure the name isn't too common, lest potential buyers go to another seller with a similar name. Second of course, are legalities. Should you eventually decide to incorporate, or purchase a domain name that reflects your identity, you want to make sure your name isn't identical or overly similar to something already in use.
Know the Legalities
There are a few restrictions that eBay imposes on selecting a user ID. Some restrictions are obvious, such as no profanity. You also need to avoid trademark or brand confusion, and you can't incorporate someone else's brand into your own ID. For example, if you sell vintage Coca Cola trays, you can't call yourself CocaColaTrays. By the same token, you probably don't want to use your own name, if it coincides with a major brand. If your last name happens to be Ford, and you sell used car parts, calling yourself FordCarParts is very likely to evoke a letter from Ford Motor Company's legal department.