Google the CARB EO number on your sticker, print it and bring it with you. Is this the right one for your kit: http://arb.ca.gov/msprog/aftermkt/de...o/D-265-7.pdf?
Make sure you have removed all the things the letter tells you to remove, and that you added all the sensors they say come with the kit, vacuum lines per the new sticker, etc.
Also, check your gas tank vents/purge system, rollover valve etc are all hooked up and the lines aren't cracked, clamps are tight, etc. He will clamp the vent line at the charcoal canister under the hood and pump like 5psi into your tank and it has too hold a % of it for a few minutes.
You may want to bring an extra gas cap in case your gas cap fails, had that happen on my last jeep.
I have the Howell kit and they gave me a hard time until I gave them that printout that matched the EO on my sticker. I had to explain why the unused port on the TBI was plugged with a vacuum line and bolt, then trace the vacuum wires for him that matched my howell sticker but he was cool after that.
The only thing they dinged me for was that for the first test I had a "snail" type air cleaner assembly that routes over the valve cover and ends with a cone type element and the letter called for an "open" air filter, but I made them run it through anyway so I would know if it would pass otherwise, since I knew I had a free retest. Came back and nailed it.
Finally, shop around for price matching and free retest or don't pass=don't pay deals.
One shop wanted over $120 bucks with no free retest but I drove 10 minutes away and did it for $54 with a free retest "if I come in right now"