At times clients want custom built booths .... etc. Building a booth from scratch, or attaching seats and backs to new booths that someone else is building, is more complicated and time consuming that just recovering what someone else has already created. When we recover a previously constructed piece of furniture the manufacturer has already figured out the details and the bugs.
Often times, when we custom build an upholsterered item, we may suggest, or require, that we make a prototype. In addition we may have to make trips to the work site, spend time consulting with the client. All this time will be billed to the client as part of the process.
In addition, sometimes the upholstered creation doesn't fit and it has to be taken part and altered.
When other people are also involved in the process of creating the project, there is more potential for things to go wrong. This is all part of the process, and any extra work will be billed to the client.