Don't be scared to be vocal about what you love.
One of my core memories as someone who was a vendor in artist alley is how much I loved seeing people from fandoms I recognized coming to my table and seeing their reactions when I talked about it. I'd only ever been on the other side of the table, so I still kept the mindset of complimenting people and asking for photos and it lead to absolutely magical interactions.
Someone cosplayed as Basil from Omori came to the table and when I complimented their flower crown, they gifted me homemade cookies. Some of the best I've ever eaten.
Someone saw my Hollow knight charms, made a HUGE smile and said "Silkong ain't coming out heh" and just. LEFT. Made me cackle real bad.
The daughter from one of the vendors complimented a watercolor of firestar I'd made during the con and she was OVERJOYED when I gifted it to her.
Someone came to my table noticing I'd been drawing a Splatoon character. We playfully argued about splatfests for a bit and after that, he was so happy bought all the merch I had of Frye and Pearl.
My friend saw a Spy x Family cosplayer on our first day and joked about that the best dad ever would be someone cosplaying as Loid and having his daughter as Anya. Guess what we saw the next morning that made me beg for photos
A little compliment can get you far when it comes to genuinely sweet human interactioon, either coming from the artist or someone looking at the art. Don't be scared to voice it up. I think it'll make everyone a little happier.