Sewer scoping as part of inspection?

[Matt Vezina]

A recent post about a landlord's cracked sewer line got me thinking about this.  I won't be in a position to purchase my first property until spring 2018 so fortunately this question is not time sensitive.

I'm curious to hear if anyone routinely does this as part of inspection on purchasing your older buildings, especially if you have had a problem revealed by scoping that led to a seller contingency.  I've been extensively researching the market until I am ready to purchase and roughly 100% of the VT multi family units in my price range are pre 1950, in some cases pre 1900 construction so likely have a sewer line that is on a "not if but when" basis for failure.  I understand this would be an additional charge above and beyond the standard home inspection but the price difference between inspection fee and replacement of a broken line is significant enough it seems like the money may be well spent.  

A few sources I've read suggested that tree root intrusion is the only problem that a scoping will catch because cast iron and clay pipes either rust or crack from the outside in, so unless the line is actually broken at time of inspection an impending break won't be seen.  If that is true my thought would be don't bother with the scoping unless there is a large tree near the line.  Appreciate any thoughts or experience, I am fairly handy with DIY stuff but not like this so a broken sewer is #1 on my list of concerns for surprise repairs.