A picture of your oddly textured/curled note would give us a better idea of what you mean but it is hard to tell whether a note has been washed simply by looking at it alone. It is better for one to feel the note to tell for sure & from your description it sounds as if it has been washed. It certainly isn't uncommon.
Washed simply means the note has been in water or has been laundered. A wet cotton-paper note dried usually loses all of its original qualities. The detergents in laundry soap will often brighten a dirty/soiled note so people used to wash their dirty notes to make them look brighter. Unfortunately, after such "processing," the note loses most of its "original" qualities. So, when one washes a note, they're actually decreasing its "collectible qualities" & thus decreasing its collectible value.
A similar unwritten rule applies to "pressing" a note. This can be simply placing the note under some books or using a warm iron & some cloth above the note. When a person presses a note all texture & embossing are removed. The colours look dull. Embossing comes from the serial number machine punching the number (indents are generally seen on the back of the note) & any other process that defines (shapes) the end product after being printed. Some note series may be slightly wavy in texture after the sheets have had their ink dry.
It is very tough to discern whether a note has been washed or pressed by seeing a scan (especially if the contrast is too high). A photo is slightly better but one needs to put up good side lighting to be sure. So, unfortunately, one relies on the honesty & good eyes of the online seller. Otherwise, if the note is pricey, it would be better to inspect the note oneself or buy TPG notes with "EPQ;" "PPQ" or "Original" designations.
For well circulated notes it is a bit easier to tell when a note has been processed. Usually one sees flattened creases and a white line (missing underprint/design) when notes have been pressed. These notes usually have been washed too & usually the underprint is too bright & the imprint (such as "Canadian Banknote Company") below the border looks impaired.
