Essentially, evaluating "common or garden" paperweights is just like anything else, "common" or not.
1) Does it catch your eye when you first see it?
2) Are you inclined to look at it a bit closer?
3) Are you tempted to check the price?
If you can answer yes to those questions, then the evaluation has been made, regardless of what anyone else may or may not say about it. All you then need to decide is whether you really like it enough to part with some money.
But also, it is wise to check out the weight from all angles, as you have done by showing a pic of the base. Then the questions start getting more particular. For instance, what is that "lump" - is it chewing gum stuck on the base? Or is it a chunk of something that is inside the glass and should not really have been there?
Even if the base shows some basic features that may not look too good, does the weight when viewed normally still look appealing? If so, then consider question three above.
Of course, by always checking the base - and all around the lower edge of the dome near the base, you may find a signature or logo of some form, sometimes quite hard to find, so can be easily missed. If there is a signature or id mark, the weight may be less of the "common or garden" variety and more towards something of interest to specialist collectors.
Also do the obvious, check the dome for scratches or blemishes of any kind. And use your fingers and palms to check the surface, too, as this can reveal tell-tale inconsistencies in the shape and finish.
Another point is that for "swirl" (and also, the similar "crown" design) weights, sometimes these are hollow blown with the base then being sealed. If the weight is very light, then it is most likely hollow. This makes little difference to the finished pattern but it is cheaper to make and should also be cheaper to buy.
Even with "common or garden" weights, do check that the design elements are well formed, be they swirls of cane lengths or millefiori slices or just abstract. Any break or misalignment detracts from the quality and should be reflected in the asking price.
It is usually unlikely that "common or garden" weights will turn out to be something of great interest and of high value to specialists, so this should really not be part of the evaluation process. But occasionally, (and as known by at least one member of this Message Board) the "ordinary" paperweight does turn out to be a true rarity.
As for your actual weight, my best guess is that it's Murano but it could also be from several makers, USA or elsewhere.