How do you define the difference between a table grape and a wine grape? Some definitions say that one is usually seedless, the other has seeds, one has firm flesh, the other is soft and juicy, one is very sweet while the other has more acid, and a few other "differences."
While those delineations hold up fairly well if you compare grocery store table grapes and classic varieties of European wine grapes, they are considerably more blurry with American grapes. Both because of the relative newness of American grapes and the state of modern winemaking.
First, look at some of the products and methods now available to alter or enhance wines. These can make some amazing differences in wines made from grapes that might otherwise be considered unsuited for wine making.
Tannin. If a wine lacks tannin to give it good body and ability to age, it can be added in pure form now.
Oak. No need to buy expensive barrels to "oak" your wine when you can steep the wine in oak chips, or even add oak extract.
Improvine the balance of sugar and acid. Acid too high? Products like Acidex will reduce the acid of a winie. Acid too low? Add chemically pure malic and tartaric acids, among others. And if needed, innoculate the wine with bacteria to produce a good malolactic fermentation to reduce the acid. Ph out of balance? Several substances available to correct THAT.
Sugar. Several types are available to boost the brix of the must.
Yeast nutrients, to help when the juice lacks something to help the yeast ferment well. If the yeast is unable to grow, there will be sugar left in the wine and you can wind up with a sweet wine when you want a dry type.
There are enzymes to clear the wine, filters to remove unwanted microflora, fliters to clear the wine, clarifiers to make the wine sparkle. And more.
With all these things, the starting grape has to be really foul to make a bad wine. Any grape with decent character can be adjusted to make reasonable wine, or even great wine.
One time I made a batch of wine from Himrod, a seedless white American grape with a pleasant fruity flavor. The grapes were low in sugar, with less than 18 degrees Brix, so the wine came out with low alcohol. At the same time, it was low in acid, so it lacked sparkle. Let's face it, in character it was hardly more than alcoholic water. However, the wine was made with nothing more than the grapes and the yeast needed to ferment them. In other words, the oldest method.
Knowing what I know now, I might have added sugar so there would be more alcohol to increase the "legs" of the wine. Adding acid would have given the wine more snap and character. Steeping some oak chips or adding tannins would increase body and complexity of the wine. By the time all these things had been done, that nondescript Himrod wine might have been taken for a crisp, dry classic wine. Or at very least, no one would have thought it was made from table grapes.
To further confuse the issue, there are American grapes like Steuben, which has large, attractive berries, and lovely spicey-sweet flavor, all of which say "table grape." And while it IS a good table grape, there are wineries in the Eastern U.S. that make very palatable red wines from Steuben. For that matter, Swenson Red. my favorite grape with it's fruity, almost aromatic flavor, and firm flesh has also been made into more than one style of wine. May that's because even though Swenson Red itself was intended to be strictly a table grape, one of it's parents, Seibel 11803, is a wine grape. While Steuben, which was actually bred as a table and juice grape, has been used in crosses with wine grapes like Baco Noir to produce good new wine grapes.
To further mix things up, some breeders have worked with breeding seedless red wine grapes. The idea in that case is to get a variety that could be crushed and pressed without getting any of the bitterness or excess tannins that seeds can contribute to a wine. A seedless red wine grape could be used to produce a red wine that would have enough tannin for good body, but little enough that the wine would age quickly and be ready to drink while still quite young. No such selections have been released yet, but that doesn't mean they won't be out sometime.
To be sure, there are many grapes designated as "wine grapes" that will probably always be used for wine only, and many grapes that will always be thought of only in terms of being eaten fresh or prepared in some way other than as wine. You aren't likely to see bunches of Cabernet grapes sold in packages in the produce section of a grocery store, and wine made from Flame Seedless isn't likely to appear on shelves in those same stores, either.
All the same, if you plan to make wine from whatever grapes you have at hand, take time to learn some of the newer wine making techniques and products to help you make something drinkable instead of being fit only to remove rust.
As far as eating grapes, your taste buds will be your best guide. There's nothing in the least bit wrong with eating and enjoying a grape fresh just because it's called a wine grape.
The fun of growing your own grapes is being able to use them any way that pleases you.