Refurbished desktop computers are worth buying as long as you buy them from a reputable seller.
I've bought refurbished desktop computers on eBay and have never had any issues.
If you're just needing a cheap computer for causal browsing, work from home etc then a good refurbished desktop computer can be good enough for most people.
I work from home and use a good refurbished desktop computer that I bought for around $100.00 from eBay and it has served me well for 2 years now.
I would buy another one if needed.
I don't do any gaming or resource intensive activities on the computer so a good refurbished desktop works for me.
If you cannot afford a new computer then a good refurbished computer will be just fine.