This is odd as most contractors are required by law to only collect a certain percentage of the contract price.
However, is this for the cost of the actual components. I can understand why payment for the "parts" would be up front.
My understanding of HD is that you buy stuff and then have the option of using their contractors to install it -- "their" contractors not actually being employees of HD.
That said, HD is a major corporation so they are highly unlikely to leave you in the lurch and paying by CC provides significant protection if they fail to perform to your satisfaction as you file a dispute.
I am more familiar with the concept of using them for kitchens -- but again one buys the cabinets and then elects whether to have them installed through them as an option. Generally the consensus for HD is that you pay more but you have the theoretical peace of mind of knowing that a corporation stands behind the installation but it's cheaper if you know a reliable installer.
Some days I pray for Silence, Some days I pray for Soul,
Some days I just pray to the God of Sex and Drums and Rock 'N' Roll.