Yes that's true , but may have only been with locals , not sure about vegas.
I used to work for a local (late 80's-eraly 90's) before most households had the internet , we had an odds service from vegas called grl sports who had these sexy voiced women that would call with line moves and steam plays , anyway , the old man would use a 1.5-2.5 run line on anything over 220 , meaning if you take the dog you get +1.5 but if you take the fav -2.5. I was utterly embarrased and felt like a heel giving those lines out. ... but people played them. ... OH , and totals at Wrigely field , Coors field , and the old Candlestick park were 200$ circles , meaning strait bets only and 200$ limit.
Hehe , i also remember the old man saying the offshores would never make it and would only be a flash in the pan b/c he said credit bettors would not put money up front.
He died in 1995 , i wish he was still around to see how things are today.