There are two types of log in milling.
1 Forest or plantation grown.
2 Everything else.
It is very important to distinguish these,
as forest trees will be very suitable for all sawmills.
Garden,hedgerow,farmers field,parks,roadside etc etc these trees will nearly always contain “inclusions” things inside the tree. By this I mean nails, bolts and washing line pulleys, barbed wire and other fencing detritus. No commercial sawmill will touch these trees.
However a chainsaw mill will just need to change a chain to continue cutting.
What logs are you looking at buying?
I buy allot of both, but normally the second option you said “everything else” is always the best logs for grain patterns etc.. also the worst for metal 😂🫣