I've noticed that lately many sellers offer free return on their framesets.
Are you sure this is something new? Are you sure it's not an oversight, but rather a FEATURE of the deal?
Because for clothing and regular items, at least in europe, you can simply say you changed your mind, and they send you return information, free of charge.
Now if that really is the same mechanism, then nothing is stopping people from frivolously buying 2 different colours of the same frame and return 1, if not both, because they can?
Does this apply to custom paint jobs as well? If so, then i'd say it's an oversight / mistake, not a feature.
Also, with regular items, you have a long time (i think at least 30, if not 45, if not 60 days?) to request a return. On Temu i think it's 60 or even 90. So if the terms are the same, you can build the bike, really stress test it, and return it if something is off. Or if you just change your mind...