Sofas, perhaps especially, are pretty hard to fit for non built-in furniture. I bought a used sofa off my brother. (Ironically, their replacements ended up being terrible because they lasted about a year with their dogs.)

I was also very lucky though. I thought I could configure the sectional in a couple different ways. Turned out I rolled the dice the right way because I couldn't. And only discovered this after many months because I was on crutches at the time and couldn't do anything about the sofa sitting in my garage.