It is strictly at the Homeowner's discretion and decision, depending on the Pet and how many. Preferrably matured, trained animal under 20 lbs is usually acceptable, with a Pet Deposit of course.

I ask first before showing anything that does not specify pets ok

I agree with Jill Murty. I would ask first. If they say it may be considered, then yes - show the property but if it is a strict "no pets allowed" policy then why waste your time showing?

Show all property and go from there.

If a renter was extremely interested in a property where the listing stated ''No pets", I would ask if a pet would be considered prior to showing the property.  Sometimes the landlord will consider a pet if the prospective renter has excellent credit, etc.  If it's a  definite 'No', there's no point in showing the property.

Landlords have rules for a reason.

If no pets are allowed why waste time.

I check the status of the pet policy first.

I only show them homes allow pets. Do not waste time.

I call the agent and ask before I show. 

Well after learning my lesson, I generally refer renters to someone else unless they pay my fee up front or plan to buy within the year.  That weeds out the unreasonable and time wasters.