[special-K]

I used to look for rust free only. As time has passed and panels now available,I'd consider a truck with "minimal rust". As mentioned, normal rust means it's rusty because it's normal for a truck to have rusted out rockers,corners,cab supports,outer floor,cowl,right front fender bottom,door bottoms,core support,inner fenders,cowl area...
Rust, mechanical condition, or whatever, if the seller doesn't give informative answers you need to walk away or go look with ears turned off and see for yourself whether it's something you want r not. Generally, the first option will be the best. It just depends on how hard you are looking.