Soil stack bend replacement

motherofcats

I was quoted £500 plus vat to replace bend of the Soil Vent Pipe along with some of the downstream pipework.
The drains person quoted and diagnosed the issue without opening anything up or putting any cameras down.
 This is in Manchester.
Is this reasonable or should I get a second opinion?

plumb1_2

Is the pipe above ground or below, post some pictures 

motherofcats

The bend is below the patio. Can't take pics just at the moment, too dark out!

grimboj

I would be suspicious if they didn't use cameras, the stench is a giveaway but it can be misleading where it's actually coming from.

£500 sounds fair for a correctly diagnosed sub-surface problem