Hmmm. John Lip and Elspet Steinson did have a daughter Margaret, born in Keith in 1781, so just about the right age to marry in 1805.
According to LIBINDX Margaret Lipp, wife of William Cruickshank, died in Rothiemay in 1862 and is buried in Keith. So it isn't going to be difficult to confirm her parentage.
Whether that is also enough to prove that her sister is the Isobel Lipp who married William Bain I am not sure. Maybe one of Isobel's children registered Margaret's death?
Wait a minute .... in 1851 Margaret Cruickshank is in the household of her great-nieces Isobella Henry, widow, born Mortlach, and Jessie Anderson, and in 1861 she is listed as Margaret Lipp in the household of Alexander Milne and his wife Isabella, born Mortlach, who is exactly 10 years older than Isobella Henry was in 1851. You can view the full details of these censuses at
http://www.freecen.org.uk/cgi/search.pl The IGI confirms that the children listed in the 1861 are those of Alexander Milne and Isabella Anderson, whose marriage on 20 November 1851 was recorded in both Grange and Rothiemay.
Now, there's a birth of Isabella, born 25 November 1825 in Mortlach, daughter of Charles Anderson and Isabel Bain. I looked on SP and was unable to resist the temptation to check the death of Isabel Bain, aged 62, in Mortlach in 1862. She was indeed the daughter of William Bain and Isobel Lipp, and wife of Charles Anderson.
I reckon that is enough to show that Isabella Lipp, wife of William Bain, was indeed the daughter of John Lipp and Elspet Steinson.
1. Lipp John
sp: Steinson Elspet (m.22 Dec 1778)
2. Lipp Isabella (b.1779-,Botriphnie,Banffshire,Scotland)
sp: Bain William (m.23 Sep 1797)
3. Bain Margaret (b.13 Jan 1798-,Keith,Banffshire,Scotland)
3. Bain Isabella (b.16 Dec 1799-,Keith,Banffshire,Scotland)
sp: Anderson Charles (m.26 Apr 1821)
4. Anderson Isabella (b.25 Nov 1825-,Mortlach,Banffshire,Scotland)
sp: Henry William (m.18 Mar 1847)
sp: Milne Alexander (m.20 Nov 1851)
5. Milne George Duncan (b.8 Sep 1852-,Rothiemay,Banffshire,Scotland)
5. Milne Alexander (b.19 Mar 1854-,Rothiemay,Banffshire,Scotland)
5. Milne Margaret (b.15 Jun 1857-,Rothiemay,Banffshire,Scotland)
5. Milne Isabella (b.12 Feb 1869-,Rothiemay,Banffshire,Scotland)
4. Anderson Elizabeth (b.27 May 1831-,Mortlach,Banffshire,Scotland)
4. Anderson James (b.1835/1836-,Mortlach,Banffshire,Scotland)
4. Anderson Jessie (b.1840/1841-,Mortlach,Banffshire,Scotland)
3. Bain John (b.15 Oct 1804-,Mortlach,Banffshire,Scotland)
3. Bain Elspet (b.27 Feb 1807-,Mortlach,Banffshire,Scotland)
3. Bain Jean (b.22 Jan 1809-,Mortlach,Banffshire,Scotland)
3. Bain James (b.1 Apr 1811-,Mortlach,Banffshire,Scotland)
3. Bain Alexander (b.3 Jan 1813-,Mortlach,Banffshire,Scotland)
3. Bain Janet (b.9 Feb 1816-,Mortlach,Banffshire,Scotland)
2. Lipp Margaret (b.23 Dec 1781-,Botriphnie,Banffshire,Scotland; d.1862-,Rothiemay,Banffshire,Scotland)
sp: Cruickshank William (m.26 May 1805)
But never trust anything you see online, unless it's an original certificate. Not even what I am saying - you need to make sure that
you have the sources and proof. You still need to follow up by checking the originals of the census, Margaret Lipp or Cruickshank's death certificate (1862), and the death certificate of Isabella Anderson or Henry or Milne.