While it looks like it is in good condition, pictures lie. For $2000, it should be running, otherwise that is a $1000 bike IF it has a clear title. No title, half that. Unfortunately these bikes are becoming increasingly popular with hipsters and it is driving the prices up. So many of these bikes are consequently snapped up at inflated prices, chopped and hacked into poorly executed cafe racers and then dumped when they can't them tuned correctly.
The problem with old two strokes sitting is the crank seals. These are rubber seals that prevent air leaks into the crankcase. When they dry out they crack and leak, causing the engine to run very lean and overheat, causing a piston seizure. Bad things. Plus the bike will run like hell until that happens. Replacing them may or may not require splitting the engine, some bikes this is necessary and others not, I am not familiar with the DT series bikes to say for certain. In addition, the oil in the oil lines from the injector pump can harden into goo, which will block fresh oil from getting to the crank bearings and piston again causing the engine to lock up. Lots of people advocate removing the oil pump and blocking off the ports, this is usually a bad idea. By the late 70's, technology had made these things dead reliable and probably one of the last parts to fail on a two stroke. Removing them could prevent oil from getting places that premixed oil/gas through the carb cannot get to like the crank bearings. Cleaning or replacement may be necessary, not a huge burden but they can be hard to find. Then the usual a old bike stuff, stuck clutch, old degraded wiring, rust, gummy fluids in the forks and transmission case, old tires, etc. It can be fun and rewarding to get one of these old bikes running properly, I enjoy it as a hobby, but it takes more than just a carb clean and an oil change.