On March 31, 2015, about 1435 eastern daylight time, an experimental light sport Just Aircraft Highlander, N376CG, was substantially damaged when it impacted trees and terrain at a private airfield near Walhalla, South Carolina. The private pilot and passenger were seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed. The local business flight was conducted under the provisions of 14 Code of Federal Regulations Part 91.The pilot was demonstrating the airplane to a potential buyer. The pilot reported that the wind was calm when they departed, but gusty when they returned about 30 minutes later. He estimated the wind as a 20-mph tailwind during final approach, gusting to a 25 to 30-mph tailwind. The airplane approached too fast and the pilot performed a go-around. He increased the engine power to full power and the airplane began to climb, but as it approached trees at the end of the runway, "a big tailwind gust" caused the airplane to cease climbing. The airplane collided with the top of the tree, descended, and impacted the ground. The pilot did not report any preimpact mechanical malfunctions. According to a witness, the accident flight was one of several flights performed to demonstrate the performance characteristics of the airplane to a potential buyer and his friend. The witness indicated that during the accident flight, the airplane was landing toward the east with a tailwind, and travelling faster than normal as it approached the runway. As the airplane descended toward the runway surface, the witness observed an increase in engine power, and the airplane subsequently "ballooned." Shortly thereafter the pilot "added full power" and the airplane began to climb and flew over a two-story building located about 100 ft east of the runway, along its extended centerline. The airplane then struck trees adjacent to the north side of the building before it impacted the ground in a wooded ravine. The witness added that the turf runway was 400 to 500 ft in length, oriented east-west. Due to sloping terrain, all landings are performed to the east and all takeoffs performed to the west. The pilot held a private pilot certificate with ratings for single-engine land, airplane single-engine sea, and instrument airplane. The pilot reported a total flight experience of 6,672 hours; of which about 46 hours were in the same make and model as the accident airplane. All 46 hours were flown during the 90-day period preceding the accident. Oconee County Regional Airport (CEU), Clemson, South Carolina was located about 10 miles east of the accident site. The recorded weather at CEU, at 1454, was: wind from 260° at 12 knots, gusting to 21 knots; visibility 10 miles; sky clear; temperature 26° C; dew point 2° C; altimeter 29.92 inches of mercury.