once buyer asks for cost of the job he needs to be done by seller, and seller mentions a particular amount, they turn down the offer instead of trying to negotiate. It’s awkward.
Perhaps the buyer asked multiple sellers, and chose the one with lowest price.
Why is that awkward? That is very common in business. When giving a quote to a potential buyer, that is all they are, a potential buyer, it does not mean they are definitely planning to buy from you. When running a business here or anywhere else, you are basically wearing a sales person hat to try and get jobs. As any salesperson understands, there is that saying you have to accept 9 no’s before you get 1 yes. I don’t think it’s that high on Fiverr, but you should just be prepared that you will not get every job you give a custom quote on.