It depends on whether your intent is to confuse people looking for the other site. If so, expect to have lawyers crawling up your **** over it. If not, and I gotta doubt that, then you have nothing to worry about.
most likely not:
EBAY71.COM is available! And I doubt ebay have "ebay71" trademark
I'd suggest you brush up on your trademark law knowledge. You don't have to register an identical name to infringe on a trademark. This is especially true if you are competing with the primary mark and if the marks are confusingly similar.