When I tried to sell items one by one at Riverrun the Game froze. ( I was trying to get my speech skills up.) I had already accept the theif catcher quest.

Riverwood *sigh*
the game does randomly freeze on occasion, nothing you can do about it but save often.

Lol riverrun

Whiterun. Riverwood.
It's like saying "I'm going to wood a bit in the runs."

And your game is most likely freezing because of a technical issue unrelated to the merchant.

Heh, lol.
It does get a bit crashy occasionally - just make sure you save.
I've noticed that Windhelm - (Windrun? ) - is bit Crashy-McCrashington sometimes...