[tim333]

There isn't really 100% proof either way so you are left looking at evidence and estimating probabilities. There is quite a lot of evidence suggesting a lab origin, for example sarbecoviruses have not been found in nature with a furin cleavage site and Ralph Baric proposed inserting one, which was put into a grant proposal by Daszak and low a year or so latter one pops up by the lab he worked with. I mean that never before seen thing could have evolved randomly at the market down the road by coincidence but it seems a low probability.