A lot depends on the bike. But, calculate the value of the fork into the cost of the frame.

If you're buying some Classic/Vintage frame, then it is always best to find one one with a matching frame/fork. Some brands like Colnago forks can be quite expensive.

A lot of MTB riders swap forks, and choose a custom fork with the characteristics they desire. So, if you're looking at MTB frames, I wouldn't have any problem at least with the concept of a forkless frame. Of course, as above, the best value may be with a matched set.

Keep in mind a missing or swapped fork can also be a sign of a crash, with the potential for frame damage.