My experience presenting designs of various levels of fidelity, is this:
If the design appears obviously incomplete or unfinished, much critical judgement is withheld since it's assumed that whatever criticism they have will be addressed by the final design. Depending on your goal, this can be helpful or even counterproductive (maybe the finished design won't be how they assume it will be). Or others will instead focus on high-level feedback like addressing the overall theme and direction instead of the minutiae of the design.
If the design appears highly polished, then any issue, however minor, is assumed to be "finalized" and thus the criticism pours out.
If you make it appear completed, then people will assume it is in fact completed. If you're still working on it, make it look clearly unfinished.
However, no matter how much you stress it is a prototype or make it look as such, someone will still criticize the the fact it's all in black and white and all the text says "Lorem ipsum".
I believe we're conditioned to understand various fidelities of information based on the principles of design. These fundamental principles—things like contrast, balance, proportion, hierarchy, motion, and variety—help us determine how to interpret what we experience.
For example: a webpage that has clear hierarchy of information, is visually balanced, uses motion to attract attention and convey concepts, is much more likely to be interpreted as a final product. Whereas a page that is a bit disorganized may be understood as in early development.
The problem is most landing pages are one page, so the creator invests considerable time in making them look and work well, leading to the perception of a complete project.
Then when the time comes to build a fully functional website/product, there's a lot more to invest in and so less time is spent.
Paradox of shipping an MVP product or business, I guess.
Some app prototyping[0] have a "sketch" style that draws wobbly lines in order to simulate this and promote this effect.
I've seen it first hand numerous times. Even if a client/audience feels the need to offer feedback/criticism ('cause they always do) the level of polish even affects how they frame the feedback/criticism.
If the design appears obviously incomplete or unfinished, much critical judgement is withheld since it's assumed that whatever criticism they have will be addressed by the final design. Depending on your goal, this can be helpful or even counterproductive (maybe the finished design won't be how they assume it will be). Or others will instead focus on high-level feedback like addressing the overall theme and direction instead of the minutiae of the design.
If the design appears highly polished, then any issue, however minor, is assumed to be "finalized" and thus the criticism pours out.
If you make it appear completed, then people will assume it is in fact completed. If you're still working on it, make it look clearly unfinished.
However, no matter how much you stress it is a prototype or make it look as such, someone will still criticize the the fact it's all in black and white and all the text says "Lorem ipsum".