That started 2008. House was paid off over 10 years. At peak those eBay resales amounted to about 5000€ annually, but mostly around 2000€ anually. That extra tax free money came a long way in paying of the loan.
Of course the government caught on to people doing that and limits the amount of private sales you can make at 2000€ a year, before having to declare it.
Luckily, by that time, my dad had gotten himself a decently paying job and didn't have to rely on that anymore, but if it wasn't for years of grinding eBay it would've probably taken twice as long.