Well, photos would go a long way to identifying the machine.
Singers are simple for the most part.
Almost all treadles are antique / vintage and require parts that are the same. If you don't want to bother with that, then why bother with it at all? Parts are not that hard to come buy and most of the old machines are fairly simple.
Diagnosis:
Look for missing parts > slide plate being the most common, feet, levers, spool pins
Look for obvious damage > finish wear on an older machine is not considered damage, considering how they were finished, it's to be expected.
Chips, rust, scratches dents, broken parts, that is damage.
Check the hand wheel, see how it turns. If it's stiff most likely it just needs cleaning and oil.
If it's most Singers the hand wheel rotates towards you.
White made machines, no matter what they are badged and the Singer 9W-7 series rotate away from you.
New Homes also rotate towards you.
Remember these machines were designed by blacksmiths and carpenters, not rocket scientists or computer geeks like the new ones.
Joe