You already have a bike from SPCycle right? So you know the basics, buy stuff from a source that tests products and creates testing reports or from a source that you can trust having looked into that stuff in the past. If you worry about this, you probably should avoid sellers who peddle in fakes and should approach with caution companies where there are multiple broken products in the small sample size of this forum. Even among the fakes, the Seraph Tan Tan X68 fork breaking is more an exception than the norm.
Regarding the actual frames themselves. I have zero worry about this with my LTK266DSL. Supposedly they benchmarked the bike in terms of stiffness against the Giant TCR. I wouldn't argue against that.
