How to tell if costs are legitimate?

there in lies you problem it was an estimate rather than a quote, a quote for a finished job is just that an agreed sum for all work, an estimate is an estimated cost and can vary on how much materials are required & how easy or how hard the job is 25% increase in materials cost seems rather high, you should always get costs of extra work required at the time, you realty only have two choices either pay him and learn from your mistakes or argue the toss and see if he will reduce the bill. its not unreasonable on your part to ask for an up to date break down to show how he has arrived at his new & final costs, it also not unreasonable to ask how he can be so far out on his material costs. as someone who uses these materials day in day out he should know roughly how much thing cost within in reason a quarter higher is a big jump. apart from the fact if doing a quote you always cover yourself by getting a quote from you suppliers to guarantee you the prices are not suddenly going to jump up on you. it all seems a bit strange. good luck Alex

This is the tradespeople moving the goal posts, but also the customer too. This can and does cause confusion. If I need to do extra work, I do it with caution and agree a price upon an extra quote for extra work. And do this by text message as to minimise confusion. As for the extra 25% add on of fees may seem steep but the tradesperson could of miss judged a product price (which is a mistake by them) or the customer asked for something else which cost more, am not sure. It isn't something I'd do after a fixed quote has been given. Unless agreed. These things do happen unfortunately. I hope you enjoy your bathroom for years to come.

This question would be impossible to answer without the tradesmans version of events. No tradesman can account for any additional materials needed and any snags they hit whilst doing the job. However, i always inform customers of the jobs progress and discuss any additional costs or problems at the earliest point. At the end of the day we do this to earn a living and provide for our familys etc, if a job over runs or materials are needed due to oversights i dont see why the tradesman should foot the bill