In The Half-Blood Prince, Harry Potter and Albus Dumbledore take 'a trip down Bob Ogden's memory lane'. Bob comes up to the Giants door, 'wearing the strange assortment of clothes so often chosen by inexperienced wizards trying to look like Muggles'.
Morfin Gaunt drops out of a tree, and starts speaking in Parseltounge. Marvolo comes outside, asks Bob if he's Muggle-Born, and says that he has the same nose as people in the village:
"Are you pure-blood?" he asked, suddenly aggressive.
...and muttered, in what was clearly supposed to be an offensive tone, "Now I come to think of it, I've seen noses like yours down in the village."
My question is, wouldn't Bob's clothes have given a hint that he was pure blood, or at least brought up with wizards?
Or, if he WAS Muggle-born, then why didn't he dress like a Muggle?