Having work performed that aids in the sale of your boat, and accepting financial responsibility, shows your level of integrity!
The cost for this can't be all that great.
In fact, this is such an easy task, you may want to do it yourself!
Your drive has "Thru Prop" exhaust, and was among the first Volvo SX series that followed the OMC Cobra.
What they want to do is examine the back flow prevention flappers.
If I were YOU, I'd want to know the condition as well.
If memory serves me, the flappers on some models were eventually eliminated!
Your system may look similar to the 5.7GLPMDA, 5.7GLPMDA, 5.7GLIMDA:
This one shows the flapper seq # 26.
Here is one whereby the flapper has been eliminated:
To inspect this area would involve removing four exhaust couplers, two elbows!
If you want to remove the risers, you could peek at the sea water transfer ports (not a bad idea to check this anyway)!
A few more minutes of time, and two new riser-to-manifold gaskets for reassembly.
If so, best to initially crack the bolts with the engine warm, IMO!
I'd ask that this be written up as though it were a service order, and describing the responsible party!
Be prepared for the expense of flappers should they NOT be in good condition (after all, it is YOUR boat!)
Get this in written form ONLY before proceeding!