Theses days I always use my own details - otherwise vital communications from the hosting company may not get sent on to you. Just be upfront with the way you do it.
If you need to host a number of sites you may like to consider a larger hosting account which can be used to host many sites - effectively becoming a "sort-of" reseller. For instance look at the awardspace click here $9.99 package - facilities for quite a lot of sites under one account.
Or consider becoming a proper reseller if you do lots of sites.
I find the free awardapace account with their 5 free subdomains (which don't involve registration of a domain name) a great way to do tests, and present work-in-progress to a client.