Yes, NO MO, NO GO.

Both are required in CA before I'll show any property.
Both are required before the seller will accept your offer.

For Buyers:

Step 1 - Jason E. Gordon 

Step 2 - Look at property

Step 3 - Write The Offer 

Not so much to show a property... proof of funds is necessary if you are making a cash or primarily cash offer. Then again, we are not primarily a multi-million dollar real estate market.

SOP in my office, since I started.   

There is no point wasting time with people who are not qualified to purchase the property they are previewing.  When/if they find out they cannot afford it, they will be disappointed, and you will be frustrated.  

The only (obvious) exception would be Open House.

Peter Mohylsky, Broker - It was always standard practice since the day I was licensed. I am no longer active; just licensed but would never recommend any agent taking someone out to show houses and consulting with prospective buyers if I didn't know they were preapproved. If they were cash buyers, I needed to see proof. Even if they were pre or approved, I'd still call the lender or the banks to make sure they was money and they had good funds. 

It's a hard and fast requirement to even meet with a potential buyer out here.  Has been so for 40+ years now.  Why waste your time showing people homes they can't afford?

In AZ, the residential purchase contract incorporates by reference the Pre-Qualification letter from the Buyer's Lender. It specifies what initial documentation the lender has received, the type of loan, the occupancy type, whether the Buyer will be relying on Seller concessions and a few more items. The Pre-Qual letter usually makes a difference when the Sellers are making a decision.

It depends on the property and seller. For most situations, I am not filtering out for lookie loo's. That said- for an offer- proof of funds is needed for all cash sales, and for financing deals- I want to see a pre-approval as well as the buyer's REBNY Financials (REBNY is our trade organization instead of NAR- and the REBNY Financials is part income statement and part balance sheet provided by the buyer stating their personal financial position).  There are situations where a broker might want to see a REBNY in advance of a showing.

Proof of funds is not commonly needed to view a house. There are exceptions...such as for high priced homes.

However, approval for the purchase is a necessity, which implies that the lender has also reviewed the buyers ability to supply a down payment and cover closing costs.

Proof of funds and preapproval must be included when making an offer to purchase.

Case by case. It's not a requirement right off the bat, but the topic will come up at some point early in the process. Occasionally a seller will require pre approval from buyers in order to show their house.

To show a property, I always ask whether a Buyer has been pre-qualified by a lender. Proof of funds and a pre-approval letter are asked for when an offer is presented. I don't believe you're going to stop lookie Lou's as there are too many agents out there willing to show unqualified Buyers properties.

Integrity in both the lender performing a thorough pre-approval and both agents requiring a thorough pre-approval would not only benefit the consumer, but strengthen the bonds between lenders & agents. Shortcuts up front are a detriment to our industry.

Yes - it is an absolute requirement! 

Yes, yet not entirely. 

Has been very common for as long as I have been around. 

Peter, it is similar to an ante in poker i.e. no ante & you are not in the game. Anyone in Real Estate, rookie or professional, agent or layman, has to do the basics or they are not a player, not real, & deserve no time of day. Exception: if they are did not know lay-people, however, once told, they get with it or not Peter Mohylsky, Broker ...This is non-negotiable with me

Absolutely, one or the other with an offer.  Just to show, only the high-end luxury properties require these.

Yes I do think it does Peter Mohylsky, Broker . It was not a requirement for our MLS but it was for me.

Yes, it's an important requirement. 

Serious agents require it.

You mean to view? Yeah or at least tell me how you're gonna pay for it in a way that I believe ya! 
For the transaction absolutely.

Peter Mohylsky, Broker in my world, it is a requirement. I do not waste my time with anyone who is not pre-approved.

To look at the houses it is not required by the listing agents, only for high end homes. Howeve4r, the buyer representation is required here and it spells how the buyer is going to pay and what they hope to purchase. 

Proof of available "green" or no showings! My time is money and I don't waste it. 

In my area, you need one or the other if making an offer. It's not required to see a home.

A preapproval or full approval letter along with proof of funds is almost always required to submit an offer in our area.  It is rare but does happen that some listing agents will require them for a showing.  I think it's ridiculous to demand it just for a showing.  It's does help to get buyerys off the fence though.

rarely for showings.  Expected with offers most of the time.

Proof of funds? Yes, absolutely. Pre-approval? That depends on your definition of pre-approval. If the application has not been approved by an underwriter i.e.written by an MLO, then it is just a piece of paper that has no meaning nor value.

Yes what's the point of wasting my valuable time if buyer is not in a position to purchase.  

Although its not required it is strongly encouraged. It definitely helps with the people who are just nosy but have no intentions of buying or selling.