ETA: The wording of that message is not from eBay - when you offer an official partial refund through a case, it shows in the case, and you get to select whether you'll accept it or not. The seller only has one shot to offer a partial, if you select no, the return proceeds as normal and the seller has to move forward with accepting it.
What is the actual capacity of the tank? Does it have anything marked on it? 350ml is twice that of 175 so the size of it should indicate a max capacity of some kind, I'd think. eg Slightly different product, but when I bought my kettle, the instructions said "fill up to 1.7L" and then on the kettle there's lines marking out capacity in 100ml increments - if those had gone up to 2L, I would trust the kettle over the instructions, IYKWIM, because that was made and tested specifically for 2L and would assume the guide is outdated.
If the capacity is clearly half what it should be for 350ml, then I'd consider a return, but I'd probably want to compare the one I got to others that are being advertised to see if there's any difference in tank size first (i.e. if you buy it from elsewhere, is the size going to be different?)
I did have something similar to this a while ago - I bough a storage shelf, that's basically a stand with racks, and then tubs slide on to it to just sorta hang there. There's medium and large size tubs, and the max weight load for each size was listed in the description, so I bought based on that (a lot of my items are really heavy, so a small tub of them can weigh a few kgs). When I read the booklet, the max capacity in that was much less than the seller had in their description.
This was concerning for me, because I don't need a large storage shelf to fail in the middle of the night, and have thousands of small parts going everywhere etc (or worse, having it topple on to someone). I contacted the seller and they just sent back a message "the manufacturer has confirmed the higher weight limit". Really not confidence inspiring. ๐ (I kept it out of sheer laziness, TBH, I'd already assembled it, and just followed the booklet specs instead). But every other seller of the same item had the same weights in their listings, too, so hard to say whether they're genuine (tested) specs or not.
