I just completed a sit and took off the sheets for washing. There was a large pee stain on the mattress. Ick!
Next time I do a pet sit, I will be removing the sheets upon arrival to check. Also take any photos if necessary. A preventative measure to avoid a potential bill or review.
On the topic of sheets and mattresses. I don’t usually check anything at the start of the sit.. I’m stuck with the results anyway is my view! I have slept in some super comfortable beds and haven’t resorted to taking my own bedding to places yet. It’s a great feeling when you have had brilliant nights’ sleep at a sit to see who made the mattress etc. I must say in Uk I find John Lewis hard to beat. I rest my case.
Wetting the bed is something I struggled with over 60 years ago.. maybe I should take incontinence pads to future sits.. I’d hate to have an accident, especially with the cost of new mattresses these days!
It reminds me of the famous book on the subject : Wet Mattress by I.P.Nightly.
When we first got our dog, we adopted her from the humane society, she slept in the bed with us. She pee’d the bed. She did this a number of times…..while sleeping. Vet visit and she had a relaxed sphincter muscle when she slept, vet put her on meds and never happened again. I guess dont assume its human urine! Ha Typically you cant get that smell out either, so it perhaps is not urine if you cant smell it. Maybe they spilled mountain dew in bed.
I have never looked at the mattress before sleeping in it at pet sits. Id be more apt to look for bed bugs than stains on the mattress. When I think about sweaty nights I’ve had from menopause, you probably wouldnt like my mattress either! 
Oh dear. I’ll never again be able to look at Mountain Dew the same way! 
I’m surprised homeowners don’t put mattress protectors on their beds.
Yes they make very comfortable and quiet waterproof mattress protectors these days! Not the crinkly plastic sheet kind I remember as a kid. Maybe worth packing if you want to be careful about the state of HOs’ mystery mattresses, they do fold up as compactly as a normal sheet. I hear some sitters like to travel with their own linens anyway.
I learned of these years ago when I was house training my dog, and I caught her jumping up to wet the bed ON PURPOSE!! She didn’t make a habit of it for very long but ever since we’ve kept up with using mattress protectors anyway. (Future prospective sitters please know that she hasn’t peed in the house since potty training and that we no longer have that mattress 
)
I sat a cat that did that, according to her humans. Happily not while I was there, but they left me a rubberized sheet to spread across the guest bed whenever I went out.
Apparently the cat once jumped up and peed on the bed while the human was standing there and watching.
OMG I haven’t heard that one since I was 5 years old !
I posted this comment about having a recent experience about a stained mattress. Fom the comments, I would like to clarify as person mentioned that the stain could be from a pet. That was not the point of my post.
I will be checking mattresses as a precaution. Potentially a homeowner may not be aware of the stain or claim that I damaged their mattress even though the stain was there previously. Replacement costs hundreds of dollars. Just an ounce of precaution.