can a buyer change the budget after placing an order?
In what way? If you mean offering to pay more for extra work, then sure, you just need to use the Extras option: https://www.fiverr.com/support/articles/360010791778-Offering-Extra-Services-within-an-Active-Order
The buyer can increase the price by buying gig extras, but there’s no way to lower the price!
Yes you can but only buyer increase the price by using extra work.
Yes he can buy extras or additional services but he cannot lower the price after purchase…
Gig extras will make it happen.
Thanks to everyone for the support
He can increase the price only…
if the buyer wants to buy any extra service from you then he/she can increase the budget with your permission but the buyer can’t lower the budget after placing order