Were the McFlys doing well for themselves?
After Marty instills more confidence in George he seems to be living an affluent life with a BMW, playing tennis at the country club I assume, an expensive piano, etc. However, they are still living in the same house and neighborhood.
The question is, how could the McFlys afford to live in that kind of neighborhood originally? They must have had solid middle class incomes in the first place. Maybe they were just scraping by and had to have old second hand furnishings.