As I have been trying to save some money for a rare 3 lamp F40T12 preheat fluorescent fixture that was supposed to be sold along with a few other slimline fixtures and a rapid start F40T12 strip on OfferUp.com, I noticed that the seller is refusing to sell me none of the fixtures simply JUST BECAUSE ONLY ONE OF THEM FELL. It really irritates me that he refuses to sell ANY of them including the preheater even though I asked him if he still had any of the fixtures. He simply said "Sorry I no longer have the fixtures available for sale". This really hurts me a lot because these 3 lamp F40T12 preheat fluorescent fixtures are rarer than hen's teeth and rocking horse waste combined and such fixtures can take DECADES to find even with the most METICULOUS SEARCHES because they were DISCONTINUED DECADES ago. The thing that really makes it rare is that it has some unique art deco diamond shaped endcaps. I had considered obtaining it since its unique design would make it a decorative addition to my living space. I fear that these fixtures are possibly even more rare thanks to possibility of it getting scrapped.

Here is where the seller started to refuse to sell me any of the fixtures:

Seller:

"Unfortunately one of the fixtures recently fell. I’m unable to confirm the working order so I’m no longer selling them."

Me:

"I am still interested in getting the 3 tube fixture though."

"I can change out the ballasts if they don't work."

"Can I still get it though?"

"Do you still have the fixtures even though you are no longer selling them?"

"If you still have any of them, I would be happy to pick up the 4 foot 3 tube fixture."

"Please let me know ASAP if you still have any of the fixtures you listed here?"

Seller:

"Sorry I no longer have the fixtures available for sale."

I really would like to know if anybody else has had similar experiences when they tried to obtain any rare lamps, fixtures, and ballasts for their collection. In addition, do you think that I should continue to do anything else if I still want to get the fixture? This is one of my worst frustrations that I have ever dealt with when trying to obtain a rare light fixture for my collection.

Here is the link to the fixture that I was attempting to obtain:

https://offerup.com/item/detail/1320574317

I'd leave it. If he doesn't want to sell them that's up to him, they're his fixtures. All you're going to do by pressuring him is make him even more determined not to sell them.

Yeah, I would leave it. As unfortunate as it sounds, sometimes you can't save everything you encounter for various different reasons.

When sellers feel pressured or intimidated by a buyer that comes on strong, there's a higher chance they'll choose to back out of the deal and move on to a new buyer. Remember deals made through online marketplaces like this can go wrong in many different ways so if the seller feels something wrong with their gut feeling they would back out to be more safe. It looks like this might be their first ad on one of these sites so they might be extra vigilant and chose to back out. 

The ad is still up so he either didn't bother to delete it if he doesn't want to sell anymore or left it up in hopes a different buyer will contact them.

The seller probably got a better price from another buyer and he found this cowardly excuse .

If you want to make sure that this is a lie and a question of price, send him an email from a fake email address and name, offering a way higher price, "Hi, I've been told that you're selling blabla for $$$$ blabla" and see if he agrees or has another excuse.

Once on eBay, I saw a fluorescent for $20 but it seemed too expensive to me.
I contacted the seller through the "Make an offer" button and he was OK to sell it for $10.
A few days later, he sent me a message like "Hi, sorry, I lost the lantern, it's somewhere in my garage but I don't find it blablabla".
Me: "It's OK, I can wait a few weeks"
The seller: "Well I really have a lot of stuff in my garage, it's really lost"
Me: "OK, no worries, let's cancel the transaction"

The lantern was back on eBay a few days later, at $20. The seller lied of course, I didn't really care, but I would have understood if he negotiated the price or told me that he changed his mind.

From what you described, it sounds like someone told them, (or they realise actually how rare it is), and withdrew the items so they can put up the tri-tube fixture on its own for 6 times the original price?

I'll be honest, this is really the type of thing you should expect from Offerup, as the  8 or 9 times I tried buying something off there, only 1 of those times was successful (which happened to be for a 3 lamp F40 preheater that was in my area along with a 4 lamp F96 strip), about 3 times I was told items were no longer for sale by sellers, 5 times I got no reply by sellers, got ghosted by one seller, and one never shipped an item after getting payment (thankfully I got a refund from that one). So I'm sorry to hear this happened, but this doesn't come as a surprise to me.

Well the original ad is now listed as sold and the seller has a new ad for just the F72 lamps now.

Yeah I think with most buy and sell sites likes it's common to expect that sometimes the seller will give you the runaround or ghost you if they get a better deal.

Yeah, stuff like this occurs on OfferUp from my experience as well.