Ask for the complete installed price
Compare whole scopes. A material option can change the equipment, delivery and labour allowed for in the quote. Ask each contractor to list these assumptions so the prices can be compared.
Check samples and transitions
Ask to see a sample or recent finished project. Look at what the wall will look like where it meets steps, fences, paths and changes in ground level.
Ask what upkeep looks like
Ask what maintenance the contractor expects and what any warranty covers. Confirm whether replacement materials can be sourced later and what you would need to keep for your records.
Build a quote request