Yes - you can file. Question is; Is it worth it?
The verbal conversation is worthless - unless they agree they said what you claim they did.
The "ok, no problem" message you received is not that strong of a warranty.
What does the receipt say that you received? Does it say anything about returning it if it fails? Does it list the serial number of the camera? If not, could the seller claim you did a swap?
Your chances of winning in small claims is 50/50. If he doesn't show to court, you may get a judgment against him, and then you have to work to find him to get payment.
Heck, call Judge Judy - it may be easier.

