If you don't trust them, take it to someone else, and have them perform a leak-down test on it. That will tell you if your rings are bad, etc. and whether or not they are right. When performing a leak-down test you can actually hear where the air is comming out, so you know what is leaking.
If your rings and valve seals ARE bad, then it's time for a performance rebuild, or SR <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
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