I'm not sure without pictures if anyone will be able to give advice.

Good point..I've posted the pictures below! Thanks

My guess is it is not the workmanship, just an old an inexpensive oak flooring and not a "select" grade. It's simply taking the stain color unevenly where grains are more open or closed. That's my guess.

What are my options?

Your options are to re sand and remove the stain and live with a natural oak toned oak floor.........or to replace it with a new version either pre finished or sand on site select oak . That's probably it. The grain is, what the grain IS. Not all oak is "equal".

Or you can try again, then wet the floor after sanding ( water popping ) to open the grain and accept a darker stain......and pray. Stain is a one coat process, you get..... what you get.

http://napervillehardwood.com/blog/what-is-water-popping/

We usually specify two coats of stain which helps to even out the color. it would help a lot to have a photo because I don't know what you mean about seeing the lines in between. We recently used 3/4 Jacobean and 1/4 Ebony on an old oak floor and it came out great. If you do apply another layer of stain, you might want to reduce the ebony. I'm attaching a photo of stain options that we looked at for a recent project. In the upper right is the 3/4 Jacobean and 1/4 Ebony. This floor has a mixture or rift and plain sawn oak and you can see a lot of variation with this one coat sample.

I would recommend keeping the light colored oak floors. Unless yours are very different than usual, light oak floors are more timeless, beautiful, and easy to care for. I do not feel the same way about dark floors. My DD jumped on the " dark floors bandwagon". They have a beautiful look....until someone drops a crumb or breathes and stirs up a speck of dust! Ugh.....awful!

I suspect it might look a lot better with a coat of finish on it. You might try that before sanding it off. It won't make the sanding any harder.

I simplified my life many years ago by quitting trying to make wood look like something it wasn't. If you choose wood that is the color you want to start with finishing becomes dramatically easier. One still has to deal with matching old work though.

It's the floors. It would have been better to not try to get those so dark. That is your problem. Accept it and move on, or replace them and move on. A second coat of stain isn't going to ever do anything that a proper first coat didn't do. Other than give you adhesion problems with your top coat. It's STAIN, not paint. It's meant to penetrate the wood, and then the stuff that doesn't penetrate gets wiped off. It doesn't bond to the wood like paint where you can just add more layers on top. You do that, and you get issues that are much bigger than you have now.

It took us multiple coats and opening the pores of the wood to get an even color for a mix of Jacobean and Ebony but our floors were Black and very even when done. Our finisher was very good and he said it was the most difficult finish he had ever tried to get. It can be done, This is what an ebonized finish is.

He says when he does this finish now he does not sand it quite as smooth as he does for standard finishes and opens the wood pores with water.

When he did ours he ended up asking us to pay an additional 50 or 60 percent because of the extra work.

Water popping is a whole different scenario to a standard stain and seal. The rough open pores of water popped wood will absorb much more than a conventionally sanded smooth floor.

Yes. He did not do water popping on our floors because when I told him about that method he was not yet a convert. He did resand to roughen it up. He said the floors could never be sanded again to a completely unstained surface. These were just topnailed oak strip though, and we achieved the even black surface we wanted.

This is a small space = super tough to get a sanding machine in there to get off ALL the old finish. I would bet dollars to doughnuts that the gold streaks are areas where the old finish was left on. This would indicate an incomplete sanding event. In a such a small space = not unheard of. It doesn't make it "right" it just gives it a reason for being.

There are some areas where the sanding is a bit rough (again...small bathroom = horrible place to sand) which is another indication of sanding concerns. And issues with sanding will cause issues with stain coverage/appearance.

To get a sense of the real stain, you may have to give this person a BIGGER space to work with. Tiny bathrooms are horrible areas to "start". Sanding is a BEAR the floors are often contaminated with LOTS OF STUFF and the small square footage really limits the ability to correct for these issues.

I would go ahead and ask for a small bedroom to be sanded and stained. That's when you look with a critical eye at his technique.

And BTW...the bathroom will need to be done again....but that should be the LAST room s/he attempts - not the first.

If the space is too small for a sanding machine you just need to downscale your equipment. I've used belt sanders with a sanding frame, random orbit sanders, detail sanders, planes, scraper planes, and card scrapers. You do have to get down on your hands and knees and do some work, but there's no reason a small floor can't be prepped properly. I actually found planes and scrapers to be faster than mechanical sanders once the spaces became too small for the belt sander.

IMO,when pros have a problem it's never the stain so that only leave's workmanship to blame. A pro should know when it's over his head BEFORE trying to do it. Otherwise if he wade's in and make's a mess,he should fix it on his own dime and not throw it in the customer's lap. In the future,adhearing to these philosophies will save some grief. Half of knowing what you are doing is knowing when to leave it alone(Klem's). Don't try to make wood look like something it isn't (rwiegand's). What to do now that you have this mess? Hire a real pro to salvage it as best he can.