See no problem with an FMF programmer, Q4 muffler and Powerbomb header as I added exactly those things after I bought mine for additional $$.
Well worth it to have them, and there are LOTS of WR-250R and WR-250X riders that use them reliably and enjoy the added performance and better throttle response.
Personally, I feel the guy's price is a bit high by a few hundred, but if you want it, you could do worse.
I'd ask the seller why the bike isn't wearing 2008 model graphics, but 2012, instead.