A few things to look at.
Check the fit of the wedge and the abutment. If the fit is bad or the abutments look badly cracked, you won't have a good fit. There isn't much you can do to fix that.
Also check the wedge. If its stuck or broken, you could be looking to some large effort.
If the wedge isn't stuck, inspect the iron for pitting. While you can buy new irons, its not often worth the expense. There are just too many good wooden planes out there in the used market.
Single irons are from a different era. They will likely be tapered in their length and may be laminated. You may be able to see where the thin hard steel is forged welded to a softer iron body. A two part iron (iron with a chipbreaker) is ok too. Once tool steel was easier to make, the makers went from thicker single irons to much thinner two piece irons.
I would say a single iron (IMHO) is more desirable, but thats a person opinion.
A bad sole or a wide open mouth can be addressed, but will take some time to fix. Patching the mouth and adding a new layer to the sole is very doable.
Slight amounts of checking in the body is surprisingly ok. Its a byproduct of the use of beech. But beech doesn't split like say oak, so you can live with some checking.
Look for a Makers Mark, not just an owners mark. Many planes that were not up to snuff were sold off without their mark. They could be of poor quality.
I'd not pay much more than $20 for an excellent example of a wooden smoother. Unless its from a good maker or appears in near perfect condition.
Hope that helps.
Jim
