If the rest of the bike was as twisted as the bars then you'd probably not notice.
If the rest of the bike was straight then I think it would be quite noticeable. I would hope that a prudent buyer would check for straightness before shelling out.
I had a 1960 Triumph T110 that was cobbled by my late brother before I inherited it.
The handlebars on that were twisted for 11 of the 12 years I had it. I only noticed when I put new bars on before selling it.
I did a canny few miles on it, but it truly was a cobbled bike. RIP
As Martyn suggests, you can get used to bars or forks being out of line. I have had the situation where it took a bike swap on a trail ride to be told my forks were twisted!
My guess is that now you know the bars are bent you will indeed notice it