I have purchased numerous bikes online. In 2016, I purchased a new 2014 Orbea Avant. I liked the frameset and the fit was good from the beginning. However, I had a lot of issues with getting the shifting right and a noisy bb. I wound up having to redo the interior cable routing to get the shifting working properly, and also wound up replacing both the bb and crank set, FSA Omega and mega exo bb. After doing those things, I have the shifting working properly and the crank set/bb, 6750 crank set and BBR-60, are smooth and quiet. I did not ride the bike much when I was having the issues. Once I did the work it became the bike I was expecting when I purchased it.
I have acquired numerous used bikes from online sources, only had one that was a disappointment when I received it. It is a Lemond Tourmalet that was in pretty poor shape, worse than I could tell from the pictures and description. I really considered returning it, but stuck with it, pretty much totally rebuilding it. I spent considerably more dollars than I wanted to, but in the end, it is now one of my favorite rides, and my favorite build that I have done.