Modern Vespa

First time I've ever seen saddlebags advertised as "for a Vespa" complete with picture https://www.amazon.com/Viking-Bags-Eagl-Scooter-Saddlebags/dp/B01K59R2CE/ref=sr_1_1?ie=UTF8&qid=1490799391&sr=8-1-spons&keywords=scooter+saddlebags&psc=1 (MV affiliate link)
I have to admit I'm tempted.

My only concern would be, unless there is some sort of pannier rack, that the paint would get worn from just general use.

They look good, but if you look at the pic, the bags are PhotoShopped onto a photo of a Vespa. With the Vespa's bulging cowls, the panniers may not fit quite that nicely. Also, nothing mentioned about attachment points.

Just sayin'

That's what big clear stickers are for.

they look nice! would be great for picnics!

I used a pair of Givi saddlebags a few years ago on a 4000-mile trip on my LX. They were a bit larger, and -- although they held a lot -- they did create a few problems.

One problem was windage; they increased the cross-section of the bike so much that fuel mileage, top speed and range were noticeably impacted.

Second, they obscured and impaired access to the center stand, making getting the bike up on the stand considerably more difficult.

NaughtyLemur is right; removable clear plastic film stickers are the secret to preventing paint damage.

I see those and all I think about are scratches.

I don't have any under seat storage on my Scarabeo and always wanted a set of the OEM panniers from Aprilia but they're nearly impossible to find. I might give these a shot. I'm concerned about the lack of tie downs though so would have to improvise something to keep them from flying up at speed. Price is right if they are in fact waterproof.

Not too bad, this is scaled to approximate size. My concern would be that they're only 4.5" deep.

You can still fit a bottle of tequila in there

I've used sports bike saddlebags on the Sport City and on the BV. Short enough not to impair use of center stand and wider but that does cause more wind resistance. Lack of tie downs wasn't an issue and I was able to put the straps between the two sides under the seat which made it very secure. The pair I used had a neoprene pad that didn't cause scratches but clear automotive film also works and few people would even notice it was applied to the cowls when the bags aren't on the scoot and can easily be removed when you aren't going to use the saddlebags for awhile.

I use Givi saddlebags, too (model #T427). They're great for all the camping gear, extra parts, etc. needed for a long trip. And the reflective stripe is very visible at night. The additional drag is a definite drawback. I overcame the obscured center stand by adding a side stand. Never bothered with the clear plastic on the cowls.

If you buy them cdwise, please post a review.

Visually, these seem like they would look good on a sportster or honda rebel. I am not a fan of soft bags, but they make a lot of sense on a scooter. There is a lot of very good luggage being made for sport bikes and modern uprights that is a little more aerodynamic and functional in terms of being able to expand and contract, that would probably work better on a Vespa.
If you want some cheap hard bags, the metal cases from Harbor freight are still about as cheap as you can get for the quality.

Panniers and load carrying are a pretty regular topic for us euro rallying Brits, so quite a few options have been tried and tested here; hard shell panniers, soft shell 'saddle bags', racks, pack racks etc. Owners put sticky plastic or rubber mesh on the legshields to prevent scratching, and work out their own rack and pack solutions. I'm pretty amazed the loads that have been mounted, but those that did Vespa World Days to Croatia in 2015, say a 2 week camping trip with all the gear, did have good cause. The GTS just seems to take it all just fine...

https://www.scooterlab.uk/gone-touring-vwd-st-tropez/

https://www.scooterlab.uk/vespa-world-days-croatia-3-sunday-sluk/

Corazzo have a universal pannier set pitched to the GTS market..
http://www.ebay.co.uk/itm/VESPA-GTS-SUPER-300-GTV-300-CORAZZO-SCOOTER-PANNIER-REAR-LUGGAGE-BAGS-POUCH-/182305969795?_trksid=p2385738.m2548.l4275

There's a hard shell system available with racking from SIP in Germany. I know of one UK couple that have fitted it and used it - just a slight adjustment to pillion 'habits' to move around it when in use..
Panniers
http://www.ebay.co.uk/itm/Case-holder-Carrier-page-Fehling-7715-Flex-Chrome-for-Vespa-GT-GTS-125-300cc-/331657863602

Quite a lot of DIY successes on MV too in the search history...

Browsing the ebay store of the company that sells the side case rack I saw rear crash bars I'd be interested in if I didn't already have some installed http://www.ebay.co.uk/itm/Crash-bar-Fall-protection-Fehling-7714-chrome-rear-Vespa-GT-GTS-125-300ccm-/232253797506?hash=item361367b482