I usually don't ride my bikes with bare butt cheeks... But, I suppose that is a risk. You can always wipe the extra brown stuff off of the seat before hopping on.

Replace the bar tape and seat if you wish and wipe the rest of the bike down with sanitizer.

You'll get some (year/season) end close-out deals, but don't expect to buy a super high end bicycle for $500, or less than the price of an Ultegra Groupset + good set of wheels. Have no doubt the vendors are playing with the numbers to make their deal and markdowns look more significant than they are.

When was the last time you ever paid "List Price" for anything at Harbor Freight?

There are good used deals out there. If one is so concerned about getting Ultegra or Dura Ace components, at fire sale prices, then buy used. But, also realize that you may be getting yesterday's technology (which sometimes shows up in the cheaper components), or components with wear, or needing cleaning/refurbishing. It just depends on the person, and what you wish to deal with.