Time to refocus and review all homes and expectations in the office before touring any more homes.

A year is my personal limit.  If after amount of time, a buyer hasn't found a home they liked, then there is an issue with their expectations. We all have different limits with sutff like this.

Perhaps switch from putting them in the car and send email alerts.

Have the buyers write out on a yellow pad their makes and breaks

Soon as you fire them they will find the perfect house

Have they been sat down to discuss to them that no home is going to be perfect and that their standards need to be lowered a bit? If this conversation has happened already, then I'd say yes, it may be time to cut the strings. If they haven't been spoken to about it in a relaxed environment that is external to their home or your guys' office, then I'd say have that dialogue first. 

Point out the cost of those months of showings and send them an invoice.

Depends. You might want to talk to them and to see what is really going on. The likely reasons: they are not ready and afraid to move forward with a purchase. Talk to them. It is obviously not about 'showing wrong houses''.

do they have an agreement with the agent?

I had one of these buyers a couple years ago, and had a heart to heart discussion about their motivation, and finally they admitted they really loved their home.

It was time long ago to evaluate the urgency of the buyers. They have none and the agent is a chaffeur and tour guide. Sit them down and have an honest discussion. Set new parameters and if they don't like it let them go. They aren't real buyers or at least not worth wasting another year with.

Yea fired three of them this year.  

What is their motivation to move? Do they have one? Charge then a refundable retainer. They get the money back when they close on a house. 

Only once did I work with buyers for about a year. Through a pregnancy, death of close relatives, etc. It was always not a good time. Even put in an offer or two. I really believed in these first time home buyers. Then they sent me a text that they were "going in another direction". They purchased a home directly from the seller and assumption of their loan. Thinking back, I don't think I would have done anything differently at the time like cutting them loose. I was working with them at the same time as I had a bunch of other clients who did come through for me, so it's probably the way the real estate cookie crumbles.

They need to be educated and cured. They have fatal mindset disease where everything they see is WRONG. What they need to know is they can create the home of their dreams from just about any property within their like field once they move in and over time. There is no perfect this is it.

Also, trading up is a good option down the line but you have to get in to trade up. You need to explore their mindset, beliefs and fears in a discussion forum. That will tell you yiour next step

Time for a meeting to review and define buyers goals and needs. It happens. I've been working with a family for over 1 year. But we've had breaks off and on where they had to " accept" facts of their buying ability, and quit thinking that every seller of a 339,000.00 home will sell for 300,000.00

Daniel Hayes It is obvious they are not serious buyers. There are buyers out there who think the next house they see is the one. It can become never ending. It's time to have a heart-to-heart with them.

It's totally your (and your buyer's agent) call.  If you don't think they'll ever buy, let them go.

A year is crazy, I guess it depends on if they are doing things serious buyers do like get a pre-approval etc. If they are just looking, I'd move on.

I would say bring them in with their agent, discuss what has been seen.  Perhaps your insight as to "there is no home without some fault" may enlighten them?  Sounds like they have not been educated on realistic expectations?