Probably 80% of shops are overbooked and work their flat rate techs over the edge, so they guess. I agree paying $80 to have a guy guess is a waste of money, and I will bet they will never admit when they make a mistake, must have uh "multiple problems". Look for a shop that isn't too busy but schedules your car in for an appointment a week or so later, they will take the time to check your car right. I am an ASE Certified Master Tech, to pass the test and get the patch requires a fair amount of knowledge. Look for certified techs at the shop you go to. Ask them what service manuals they use. Mitchell1 Ondemand 5 or ALLDATA are the right answers as they are subscription based and up to date. Ask if they are an IATN member. If they look confused keep shopping. Anyone can be wrong, diagnostic shops that care stack the odds in their favor.
Here's a story of my wifes 2007 Chrysler T&C minivan (same as Dodge Caravan) - the ABS light came on. I drove the van and noticed the rear wheel bearings were howling really bad. Code said LR Wheel speed zero. Data stream confirmed that the right rear read fine and the left rear read 0. I put in 2 new wheel bearings due to teh noise and figured it would fix itself and the noise went away, but the light stayed on. Hmm, I checked the wires where they go through the floor grommet, inspected all the pinch points really well, and I replaced the left rear wheel speed sensor next, because it was still reading zero. Light still on. HUH? now what. More better research revealed that Chrysler switched the right and left wheel speed connectors on the assembly line. I tested the WRONG side (right rear) and sure enough the right speed sensor was bad. Scanner said left rear was bad, right was fine. It didn't lie, the van was put together wrong. No problem I just installed the left rear that I replaced earlier. If I was smarter I would have tested all the sensors before buying one, but this is the Wife's car and she doesn't like it on the lift for too long so I made an educated guess and guessed wrong. Think of what can happen with more complicated systems. The chance for error is high. Smitty is right your best bet is to drive a '94 and avoid the OBDII