is it customary for new home buyers to sign over the gst,sst and rst rebates back to the builder

Is it?....Builders have pre-printed “Offer/Contract” with all the Terms and Conditions..., prepared by their own legal team, and to benefit principally the interest of the builder.
That is why, the Buyer should always consult his/her own real estate lawyer, make any necessary changes, before signing the above.

Yes, it is customary for the builder to have a buyer sign sign for rebate to the builder...the builder has the HST built into the price and qualifies for the rebate not the buyer.

Yes absolutely :) Remember HST is 13% - a pretty penny on a home purchase and not something you would be paying if you bought resale (even if you bought a home that was six months old for example) - I can explain the benefits of buying a "new" resale a little more in depth if you wish at your convenience :) Cheers

Builders are very competitive when pricing their homes and they use the rebates to keep the price down. Therefor it is necessary to sign the rebates over to them. I sell new estate homes currently and I was involved with the pricing of every model. We looked at every aspect to keep the costs and price as low as we possibly could while still delivering a high quality product. The HST made it more difficult to compete with resale homes so the rebate must be signed back to the builder.