Make very sure you’re buying the real thing and not a modded 1300 with paperwork from a totalled RS. Expert help is a good idea.
By the same token, be wary of cars with sketchy history files. They’ve always been owned by enthusiasts so expect plenty of paperwork.
Unless the price is right, make sure the engine is in tip-top condition; rebuilding a BDA can be a very expensive exercise.
As with all fast Fords it’s not unusual to find mods. Talk to those in the know to find out what affects value and what’s considered OK
As with all rear-drive Escorts rust is a big enemy, so check the integrity of the shell and the quality of past repair work.