How can i know if an antique dealer is honest?

I have some old stuff to sell which a got at a boot sale. i've been told they could be valuable.
i am going to take them to a dealer but how can a tell, or make sure he wont rip me off.
and what are the signs of valuable silver....the stamp marks?
Update: CHRIS.......i did not rip anyone off. i bought them because they looked nice. it wasn't until two weeks later when a friend saw them that she said they could be worth something. i dont think we're talking thousands here. so until you know the facts shut your mouth moron
Update 2: Chris... thats right...go for the "truth hurts" outburst. whats wrong, not used to people talking back to you. and by the way moron, i have a job. full time, would you believe.
whats your excuse for being on here? billy no mates??
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