You decide what terms you are willing to work for and they decide if they accept. At that point you have agreement or you don't
I always advocate QUALIFYING customers before you decide if you are going to pursue their project.
The qualification process is having a discussion about their needs and if they will accept the terms you set or if you will accept the terms they require or if both are negotiable to a point where agreement can be reached.
With all due respect, there really is no right or wrong unless it is illegal or unethical and you have integrity. It all comes down to having a meeting of the minds on terms each party is willing to agree to.
Both sides need to be willing to accept the offer of the other. Sometimes it is give and take and other times it is more one sided. It all comes down to who needs or wants it more.
If everyone else does it one way and you don't want to, they may say no thanks because it's a deal killer for them. if they can live with it even if you are the only one then you will be able to make a deal.
Some contractors care what standard industry practice is and others are unphased by that and demand certain terms or they say buzz off. These are your decision if they are legal and you will base it on your business goals, practical realities and your non-negotiable terms.
Right or wrong if it is not illegal is rather goofy wording for your question. Asking what standard industry practice is in an area of the world and in a given trade is much more accurate to what I think you are asking. "Is it wrong" according to who?
The bottom line if it is legal is it is up to you what terms you are willing to work for and up to them what terms they are willing to accept.
If it is illegal then like 480sparky pointed out, yea it's "wrong"
Is it wrong to ask for at least a 35% deposit before work commences?