Sorry for the length everyone, but I still can't believe my luck.
I've been looking to get a Darth Maul FX Lightsaber to take apart and use the hilt to make a full hilt version of my Battle Damaged saber. Late last week, I ended up contacting an ebay member that sells a lot of 'customer returns' to find out if they had any that were not functioning since I really only needed them for the hilts. They responded to me that they indeed had 2 that they were looking to get rid of. One of them did not have a battery pack and the other had a battery pack that 'could not be removed' they told me. They also didn't have the caps on the end that hold the battery packs in, so they said that they would throw in two of the connection pieces that create the double bladed versions. I ended up negotiating a price of $15 each + $15 shipping.
I received these today. They are in excellent condition. Both hilts have scratches you wouldn't notice unless you were really looking hard, and the blades show no signs of damage at all. So on a hunch, I took the battery pack from one of my BD DM sabers, threw some batteries in it, and put it in the one saber that didn't come with a batter pack. I flipped the switch and it fired up immediately! The blade is in perfect shape (no dead spots). I have since gotten a hold of Master Replicas and they are sending me a replacement battery pack... So basically I obtained one Battle Damaged Darth Maul FX saber for $15

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I then grabbed the one with the battery pack stuck in it. Using some needle nose pliers, I pulled the battery pack out with relative ease. The reason it was stuck was because the previous owner wrapped a rubber band around it for some reason and then put it in the hilt. I'm going to assume that they lost the end cap and the rubber band was holding the battery pack in place. Regardless, I put in some fresh batteries, popped the battery pack back in the hilt, and presto, it fired up immediately! Again, the blade is in near perfect shape (I found one small ring near the very top of the blade that looks dead), and the sound and effects work perfectly with that battery pack. So that's a second BD DM saber for $15

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But now here's the dilemma. I still want to create a single blade, full hilt version of this saber. But now I have two perfectly working double bladed DM FX lightsabers. I'm going to have to consciously destroy one of them to make my little experiment work. I didn't care when I thought that two of the sabers didn't work, but now I'm going to bust apart one of them, and it's something that would have normally run me $70-$120.
Also, there's the question of whether or not I say anything to the seller. They sold them to me for $15 each thinking that they didn't work. Now I've found out that they work just fine. They could have turned these around for a nice little profit, but instead do I treat this as 'their loss is my gain'?! I know that Christmas is a time for giving, but I don't think that they would have given me a $200 item for $30 had they really known it worked... Am I just thinking too much into this, or should I even consider returning them?
Thoughts? What would y'all do?